/**
 * 
 */

// header {{{
#include <bits/stdc++.h>
using namespace std;

using i8   = int8_t;
using u8   = uint8_t;
using i16  = int16_t;
using u16  = uint16_t;
using i32  = int32_t;
using u32  = uint32_t;
using i64  = int64_t;
using u64  = uint64_t;
#ifdef __SIZEOF_INT128__
using i128 = __int128;
using u128 = unsigned __int128;
#endif

using f32  = float;
using f64  = double;
using f80  = __float80;
using f128 = __float128;
// }}}

template<typename T> constexpr T PROCON_INF();
template<> constexpr i64 PROCON_INF<i64>() { return 1'010'000'000'000'000'000LL; }
template<> constexpr f64 PROCON_INF<f64>() { return 1e100; }

constexpr i64 INF  = PROCON_INF<i64>();
constexpr f64 FINF = PROCON_INF<f64>();

constexpr i64 MOD = 1'000'000'007LL;

constexpr f64 EPS = 1e-12;

constexpr f64 PI = 3.14159265358979323846;

// util {{{
#define FOR(i, start, end) for(i64 i = (start), i##_end=(end); i < i##_end; ++i)
#define REP(i, n) FOR(i, 0, n)

#define ALL(f,c,...) (([&](decltype((c)) cccc) { return (f)(std::begin(cccc), std::end(cccc), ## __VA_ARGS__); })(c))
#define SLICE(f,c,l,r,...) (([&](decltype((c)) cccc, decltype((l)) llll, decltype((r)) rrrr) {\
    auto iiii = llll <= rrrr ? std::begin(cccc)+llll : std::end(cccc);\
    auto jjjj = llll <= rrrr ? std::begin(cccc)+rrrr : std::end(cccc);\
    return (f)(iiii, jjjj, ## __VA_ARGS__);\
})(c,l,r))

#define GENERIC(f) ([](auto&&... args) -> decltype(auto) { return (f)(std::forward<decltype(args)>(args)...); })

template<typename F>
class FixPoint {
public:
    explicit constexpr FixPoint(F&& f) : f_(forward<F>(f)) {}

    template<typename... Args>
    constexpr decltype(auto) operator()(Args&&... args) const {
        return f_(*this, forward<Args>(args)...);
    }

private:
    const F f_;
};

template<typename F>
decltype(auto) FIX(F&& f) {
    return FixPoint<F>(forward<F>(f));
}

template<typename C>
i64 SIZE(const C& c) { return static_cast<i64>(c.size()); }

template<typename T, size_t N>
i64 SIZE(const T (&)[N]) { return static_cast<i64>(N); }

bool is_odd (i64 x) { return x % 2 != 0; }
bool is_even(i64 x) { return x % 2 == 0; }

template<typename T> i64 cmp(T x, T y) { return (y<x) - (x<y); }
template<typename T> i64 sgn(T x) { return cmp(x, T(0)); }

i64 ipow(i64 x, i64 e) {
    assert(e >= 0);
    i64 res = 1;
    REP(_, e) {
        res *= x;
    }
    return res;
}

// Haskell の divMod と同じ
pair<i64,i64> divmod(i64 a, i64 b) {
    i64 q = a / b;
    i64 r = a % b;
    if((b>0 && r<0) || (b<0 && r>0)) {
        --q;
        r += b;
    }
    return {q,r};
}

i64 div_ceil(i64 a, i64 b) {
    i64 q = a / b;
    i64 r = a % b;
    if((b>0 && r>0) || (b<0 && r<0))
        ++q;
    return q;
}

i64 div_floor(i64 a, i64 b) {
    return divmod(a,b).first;
}

i64 modulo(i64 a, i64 b) {
    return divmod(a,b).second;
}

bool feq(f64 x, f64 y, f64 eps=EPS) {
    return fabs(x-y) < eps;
}

template<typename T, typename U>
bool chmax(T& xmax, const U& x) {
    if(xmax < x) {
        xmax = x;
        return true;
    }
    return false;
}

template<typename T, typename U>
bool chmin(T& xmin, const U& x) {
    if(x < xmin) {
        xmin = x;
        return true;
    }
    return false;
}

template<typename ForwardIt, typename T, typename Comp=less<>>
ForwardIt bsearch_find(ForwardIt first, ForwardIt last, const T& x, Comp comp={}) {
    auto it = lower_bound(first, last, x, comp);
    if(it == last || comp(x,*it)) return last;
    return it;
}

// x 未満の最後の要素
template<typename BidiIt, typename T, typename Comp=less<>>
BidiIt bsearch_lt(BidiIt first, BidiIt last, const T& x, Comp comp={}) {
    auto it = lower_bound(first, last, x, comp);
    if(it == first) return last;
    return prev(it);
}

// x 以下の最後の要素
template<typename BidiIt, typename T, typename Comp=less<>>
BidiIt bsearch_le(BidiIt first, BidiIt last, const T& x, Comp comp={}) {
    auto it = upper_bound(first, last, x, comp);
    if(it == first) return last;
    return prev(it);
}

// x より大きい最初の要素
template<typename BidiIt, typename T, typename Comp=less<>>
BidiIt bsearch_gt(BidiIt first, BidiIt last, const T& x, Comp comp={}) {
    return upper_bound(first, last, x, comp);
}

// x 以上の最初の要素
template<typename BidiIt, typename T, typename Comp=less<>>
BidiIt bsearch_ge(BidiIt first, BidiIt last, const T& x, Comp comp={}) {
    return lower_bound(first, last, x, comp);
}

template<typename InputIt>
auto SUM(InputIt first, InputIt last) {
    using T = typename iterator_traits<InputIt>::value_type;
    return accumulate(first, last, T());
}

template<typename ForwardIt, typename UnaryOperation>
ForwardIt transform_self(ForwardIt first, ForwardIt last, UnaryOperation op) {
    return transform(first, last, first, op);
}

template<typename C>
void UNIQ(C& c) {
    c.erase(ALL(unique,c), end(c));
}

template<typename T, typename F>
enable_if_t<rank<T>::value==0> ARRAY_FOREACH(T& e, F f) {
    f(e);
}

template<typename Array, typename F>
enable_if_t<rank<Array>::value!=0> ARRAY_FOREACH(Array& ary, F f) {
    for(auto& e : ary)
        ARRAY_FOREACH(e, f);
}

template<typename Array, typename U>
enable_if_t<rank<Array>::value!=0> ARRAY_FILL(Array& ary, const U& v) {
    ARRAY_FOREACH(ary, [&v](auto& e) { e = v; });
}

template<typename BinaryFunc, typename UnaryFunc>
auto ON(BinaryFunc bf, UnaryFunc uf) {
    return [bf,uf](const auto& x, const auto& y) {
        return bf(uf(x), uf(y));
    };
}

template<typename F>
auto LT_ON(F f) { return ON(less<>(), f); }

template<typename F>
auto GT_ON(F f) { return ON(greater<>(), f); }

struct IDENTITY {
    template<typename T>
    constexpr T&& operator()(T&& x) const noexcept {
        return forward<T>(x);
    }
};

char digit_chr(i64 n) {
    return static_cast<char>('0' + n);
}

i64 digit_ord(char c) {
    return c - '0';
}

char lower_chr(i64 n) {
    return static_cast<char>('a' + n);
}

i64 lower_ord(char c) {
    return c - 'a';
}

char upper_chr(i64 n) {
    return static_cast<char>('A' + n);
}

i64 upper_ord(char c) {
    return c - 'A';
}

// 出力は operator<< を直接使わず、このテンプレート経由で行う
// 提出用出力とデバッグ用出力を分けるため
template<typename T>
struct Formatter {
    static ostream& write_str(ostream& out, const T& x)  { return out << x; }
    static ostream& write_repr(ostream& out, const T& x) { return out << x; }
};

template<typename T>
ostream& WRITE_STR(ostream& out, const T& x) {
    return Formatter<T>::write_str(out, x);
}

template<typename T>
ostream& WRITE_REPR(ostream& out, const T& x) {
    return Formatter<T>::write_repr(out, x);
}

template<typename InputIt>
ostream& WRITE_JOIN_STR(ostream& out, InputIt first, InputIt last, const string& sep) {
    while(first != last) {
        WRITE_STR(out, *first++);
        if(first != last)
            out << sep;
    }
    return out;
}

template<typename InputIt>
ostream& WRITE_JOIN_REPR(ostream& out, InputIt first, InputIt last, const string& sep) {
    while(first != last) {
        WRITE_REPR(out, *first++);
        if(first != last)
            out << sep;
    }
    return out;
}

template<typename InputIt>
ostream& WRITE_RANGE_STR(ostream& out, InputIt first, InputIt last) {
    return WRITE_JOIN_STR(out, first, last, " ");
}

template<typename InputIt>
ostream& WRITE_RANGE_REPR(ostream& out, InputIt first, InputIt last) {
    out << "[";
    WRITE_JOIN_REPR(out, first, last, ", ");
    out << "]";
    return out;
}

template<typename T>
void FROM_STR(const string& s, T& x) {
    istringstream in(s);
    in >> x;
}

template<typename T>
string TO_STR(const T& x) {
    ostringstream out;
    WRITE_STR(out, x);
    return out.str();
}

template<typename T>
string TO_REPR(const T& x) {
    ostringstream out;
    WRITE_REPR(out, x);
    return out.str();
}

template<typename InputIt>
string RANGE_TO_STR(InputIt first, InputIt last) {
    ostringstream out;
    WRITE_RANGE_STR(out, first, last);
    return out.str();
}

template<typename InputIt>
string RANGE_TO_REPR(InputIt first, InputIt last) {
    ostringstream out;
    WRITE_RANGE_REPR(out, first, last);
    return out.str();
}

template<typename InputIt>
string JOIN(InputIt first, InputIt last, const string& sep) {
    ostringstream out;
    WRITE_JOIN_STR(out, first, last, sep);
    return out.str();
}

template<>
struct Formatter<i64> {
    static ostream& write_str(ostream& out, i64 x) {
        return out << x;
    }
    static ostream& write_repr(ostream& out, i64 x) {
        if(x == INF) return out << "INF";
        if(x == -INF) return out << "-INF";
        return out << x;
    }
};

template<>
struct Formatter<f64> {
    static ostream& write_str(ostream& out, f64 x) {
        return out << x;
    }
    static ostream& write_repr(ostream& out, f64 x) {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wfloat-equal"
        if(x == FINF) return out << "FINF";
        if(x == -FINF) return out << "-FINF";
#pragma GCC diagnostic pop
        return out << x;
    }
};

template<typename T>
struct Formatter<vector<T>> {
    static ostream& write_str(ostream& out, const vector<T>& v) {
        return WRITE_RANGE_STR(out, begin(v), end(v));
    }
    static ostream& write_repr(ostream& out, const vector<T>& v) {
        out << "vector";
        return WRITE_RANGE_REPR(out, begin(v), end(v));
    }
};

template<typename T1, typename T2>
struct Formatter<pair<T1,T2>> {
    static ostream& write_str(ostream& out, const pair<T1,T2>& p) {
        WRITE_STR(out, p.first);
        out << ' ';
        WRITE_STR(out, p.second);
        return out;
    }
    static ostream& write_repr(ostream& out, const pair<T1,T2>& p) {
        out << "(";
        WRITE_REPR(out, p.first);
        out << ",";
        WRITE_REPR(out, p.second);
        out << ")";
        return out;
    }
};

template<typename... TS>
struct Formatter<tuple<TS...>> {
    template<size_t I=0, enable_if_t<I == sizeof...(TS), nullptr_t> = nullptr>
    static ostream& write_str_impl(ostream& out, const tuple<TS...>&) {
        return out;
    }
    template<size_t I=0, enable_if_t<I < sizeof...(TS), nullptr_t> = nullptr>
    static ostream& write_str_impl(ostream& out, const tuple<TS...>& t) {
        if(I != 0) out << ' ';
        WRITE_STR(out, get<I>(t));
        return write_str_impl<I+1>(out, t);
    }

    template<size_t I=0, enable_if_t<I == sizeof...(TS), nullptr_t> = nullptr>
    static ostream& write_repr_impl(ostream& out, const tuple<TS...>&) {
        if(sizeof...(TS) == 0) out << "(";
        return out << ")";
    }
    template<size_t I=0, enable_if_t<I < sizeof...(TS), nullptr_t> = nullptr>
    static ostream& write_repr_impl(ostream& out, const tuple<TS...>& t) {
        if(I == 0)
            out << "(";
        else
            out << ",";
        WRITE_REPR(out, get<I>(t));
        return write_repr_impl<I+1>(out, t);
    }

    static ostream& write_str(ostream& out, const tuple<TS...>& t) {
        return write_str_impl(out, t);
    }
    static ostream& write_repr(ostream& out, const tuple<TS...>& t) {
        return write_repr_impl(out, t);
    }
};

template<typename T>
void RD(T& x) {
    cin >> x;
#ifdef PROCON_LOCAL
    assert(cin);
#endif
}

template<typename T>
void RD(vector<T>& v, i64 n) {
    v.reserve(n);
    REP(_, n) {
        T e; RD(e);
        v.emplace_back(e);
    }
}

void PRINT() {}

template<typename T, typename... TS>
void PRINT(const T& x, const TS& ...args) {
    WRITE_STR(cout, x);
    if(sizeof...(args)) {
        cout << ' ';
        PRINT(args...);
    }
}

template<typename... TS>
void PRINTLN(const TS& ...args) {
    PRINT(args...);
    cout << '\n';
}

[[noreturn]] void EXIT() {
#ifdef PROCON_LOCAL
    cerr.flush();
#endif
    cout.flush();
    _Exit(0);
}

template<typename T>
void DBG_IMPL(i64 line, const char* expr, const T& value) {
#ifdef PROCON_LOCAL
    cerr << "[L " << line << "]: ";
    cerr << expr << " = ";
    WRITE_REPR(cerr, value);
    cerr << "\n";
#endif
}

template<typename T, size_t N>
void DBG_ARRAY_IMPL(i64 line, const char* expr, const T (&ary)[N]) {
#ifdef PROCON_LOCAL
    cerr << "[L " << line << "]: ";
    cerr << expr << " = ";
    WRITE_RANGE_REPR(cerr, begin(ary), end(ary));
    cerr << "\n";
#endif
}

template<typename InputIt>
void DBG_RANGE_IMPL(i64 line, const char* expr1, const char* expr2, InputIt first, InputIt last) {
#ifdef PROCON_LOCAL
    cerr << "[L " << line << "]: ";
    cerr << expr1 << "," << expr2 << " = ";
    WRITE_RANGE_REPR(cerr, first, last);
    cerr << "\n";
#endif
}

#define DBG(expr) DBG_IMPL(__LINE__, #expr, (expr))
#define DBG_ARRAY(expr) DBG_ARRAY_IMPL(__LINE__, #expr, (expr))
#define DBG_RANGE(first,last) DBG_RANGE_IMPL(__LINE__, #first, #last, (first), (last))

#define PAIR  make_pair
#define TUPLE make_tuple
// }}}

// init {{{
struct ProconInit {
    static constexpr int IOS_PREC = 15;
    static constexpr bool AUTOFLUSH = false;

    ProconInit() {
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(IOS_PREC);
#ifdef PROCON_LOCAL
        cerr << fixed << setprecision(IOS_PREC);
#endif
        if(AUTOFLUSH)
            cout << unitbuf;
    }
} PROCON_INIT;
// }}}

// container {{{

// BoolArray {{{
class BoolArray {
public:
    using value_type      = bool;
    using reference       = value_type&;
    using const_reference = const value_type&;
    using iterator        = value_type*;
    using const_iterator  = const value_type*;
    using difference_type = ptrdiff_t;
    using size_type       = size_t;

    using reverse_iterator       = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;

    BoolArray() : BoolArray(0) {}
    explicit BoolArray(size_t n) : BoolArray(n,false) {}
    BoolArray(size_t n, bool value) : size_(n), data_(new bool[n]) {
        ALL(fill, *this, value);
    }

    BoolArray(initializer_list<bool> init) : size_(init.size()), data_(new bool[size_]) {
        ALL(copy, init, begin());
    }

    template<typename InputIt>
    BoolArray(InputIt first, InputIt last) {
        deque<bool> tmp(first, last);
        size_ = tmp.size();
        data_ = new bool[size_];
        ALL(copy, tmp, begin());
    }

    BoolArray(const BoolArray& other) : size_(other.size_), data_(new bool[size_]) {
        ALL(copy, other, begin());
    }

    BoolArray(BoolArray&& other) noexcept : size_(other.size_), data_(other.data_) {
        other.data_ = nullptr;
    }

    BoolArray& operator=(const BoolArray& other) {
        if(this == &other) return *this;
        if(!data_ || size_ < other.size_) {
            delete[] data_;
            data_ = new bool[other.size_];
        }
        size_ = other.size_;
        ALL(copy, other, begin());
        return *this;
    }

    BoolArray& operator=(BoolArray&& other) noexcept {
        if(this == &other) return *this;
        size_ = other.size_;
        data_ = other.data_;
        other.data_ = nullptr;
    }

    BoolArray& operator=(initializer_list<bool> init) {
        if(!data_ || size_ < init.size()) {
            delete[] data_;
            data_ = new bool[init.size()];
        }
        size_ = init.size();
        ALL(copy, init, begin());
        return *this;
    }

    void swap(BoolArray& other) noexcept {
        std::swap(size_, other.size_);
        std::swap(data_, other.data_);
    }

    ~BoolArray() {
        delete[] data_;
        data_ = nullptr;
    }

    bool      empty()    const noexcept { return size_ == 0; }
    size_type size()     const noexcept { return size_; }
    size_type max_size() const noexcept { return 1'010'000'000; }

    iterator       begin()        noexcept { return data_; }
    const_iterator begin()  const noexcept { return data_; }
    const_iterator cbegin() const noexcept { return data_; }

    iterator       end()        noexcept { return data_+size_; }
    const_iterator end()  const noexcept { return data_+size_; }
    const_iterator cend() const noexcept { return data_+size_; }

    reverse_iterator       rbegin()        noexcept { return reverse_iterator(end()); }
    const_reverse_iterator rbegin()  const noexcept { return const_reverse_iterator(end()); }
    const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator(end()); }

    reverse_iterator       rend()        noexcept { return reverse_iterator(begin()); }
    const_reverse_iterator rend()  const noexcept { return const_reverse_iterator(begin()); }
    const_reverse_iterator crend() const noexcept { return const_reverse_iterator(begin()); }

    reference       operator[](size_type pos)       { return data_[pos]; }
    const_reference operator[](size_type pos) const { return data_[pos]; }

    bool*       data()       noexcept { return data_; }
    const bool* data() const noexcept { return data_; }

private:
    size_t size_;
    bool*  data_;
};

void swap(BoolArray& lhs, BoolArray& rhs) noexcept { lhs.swap(rhs); }

bool operator==(const BoolArray& lhs, const BoolArray& rhs) {
    return equal(begin(lhs), end(lhs), begin(rhs), end(rhs));
}
bool operator!=(const BoolArray& lhs, const BoolArray& rhs) { return !(lhs == rhs); }

bool operator<(const BoolArray& lhs, const BoolArray& rhs) {
    return lexicographical_compare(begin(lhs), end(lhs), begin(rhs), end(rhs));
}
bool operator> (const BoolArray& lhs, const BoolArray& rhs) { return rhs < lhs; }
bool operator<=(const BoolArray& lhs, const BoolArray& rhs) { return !(rhs < lhs); }
bool operator>=(const BoolArray& lhs, const BoolArray& rhs) { return !(lhs < rhs); }
// }}}

// set/map/multiset/multimap search {{{
// set {{{
template<typename T, typename Comp>
auto set_lt(set<T,Comp>& s, const T& x) {
    auto it = s.lower_bound(x);
    if(it == begin(s)) return end(s);
    return prev(it);
}

template<typename T, typename Comp>
auto set_lt(const set<T,Comp>& s, const T& x) {
    auto it = s.lower_bound(x);
    if(it == begin(s)) return end(s);
    return prev(it);
}

template<typename T, typename Comp>
auto set_le(set<T,Comp>& s, const T& x) {
    auto it = s.upper_bound(x);
    if(it == begin(s)) return end(s);
    return prev(it);
}

template<typename T, typename Comp>
auto set_le(const set<T,Comp>& s, const T& x) {
    auto it = s.upper_bound(x);
    if(it == begin(s)) return end(s);
    return prev(it);
}

template<typename T, typename Comp>
auto set_gt(set<T,Comp>& s, const T& x) {
    return s.upper_bound(x);
}

template<typename T, typename Comp>
auto set_gt(const set<T,Comp>& s, const T& x) {
    return s.upper_bound(x);
}

template<typename T, typename Comp>
auto set_ge(set<T,Comp>& s, const T& x) {
    return s.lower_bound(x);
}

template<typename T, typename Comp>
auto set_ge(const set<T,Comp>& s, const T& x) {
    return s.lower_bound(x);
}
// }}}
// map {{{
template<typename K, typename V, typename Comp>
auto map_lt(map<K,V,Comp>& m, const K& x) {
    auto it = m.lower_bound(x);
    if(it == begin(m)) return end(m);
    return prev(it);
}

template<typename K, typename V, typename Comp>
auto map_lt(const map<K,V,Comp>& m, const K& x) {
    auto it = m.lower_bound(x);
    if(it == begin(m)) return end(m);
    return prev(it);
}

template<typename K, typename V, typename Comp>
auto map_le(map<K,V,Comp>& m, const K& x) {
    auto it = m.upper_bound(x);
    if(it == begin(m)) return end(m);
    return prev(it);
}

template<typename K, typename V, typename Comp>
auto map_le(const map<K,V,Comp>& m, const K& x) {
    auto it = m.upper_bound(x);
    if(it == begin(m)) return end(m);
    return prev(it);
}

template<typename K, typename V, typename Comp>
auto map_gt(map<K,V,Comp>& m, const K& x) {
    return m.upper_bound(x);
}

template<typename K, typename V, typename Comp>
auto map_gt(const map<K,V,Comp>& m, const K& x) {
    return m.upper_bound(x);
}

template<typename K, typename V, typename Comp>
auto map_ge(map<K,V,Comp>& m, const K& x) {
    return m.lower_bound(x);
}

template<typename K, typename V, typename Comp>
auto map_ge(const map<K,V,Comp>& m, const K& x) {
    return m.lower_bound(x);
}
// }}}
// multiset {{{
template<typename T, typename Comp>
auto set_lt(multiset<T,Comp>& s, const T& x) {
    auto it = s.lower_bound(x);
    if(it == begin(s)) return end(s);
    return prev(it);
}

template<typename T, typename Comp>
auto set_lt(const multiset<T,Comp>& s, const T& x) {
    auto it = s.lower_bound(x);
    if(it == begin(s)) return end(s);
    return prev(it);
}

template<typename T, typename Comp>
auto set_le(multiset<T,Comp>& s, const T& x) {
    auto it = s.upper_bound(x);
    if(it == begin(s)) return end(s);
    return prev(it);
}

template<typename T, typename Comp>
auto set_le(const multiset<T,Comp>& s, const T& x) {
    auto it = s.upper_bound(x);
    if(it == begin(s)) return end(s);
    return prev(it);
}

template<typename T, typename Comp>
auto set_gt(multiset<T,Comp>& s, const T& x) {
    return s.upper_bound(x);
}

template<typename T, typename Comp>
auto set_gt(const multiset<T,Comp>& s, const T& x) {
    return s.upper_bound(x);
}

template<typename T, typename Comp>
auto set_ge(multiset<T,Comp>& s, const T& x) {
    return s.lower_bound(x);
}

template<typename T, typename Comp>
auto set_ge(const multiset<T,Comp>& s, const T& x) {
    return s.lower_bound(x);
}
// }}}
// multimap {{{
template<typename K, typename V, typename Comp>
auto map_lt(multimap<K,V,Comp>& m, const K& x) {
    auto it = m.lower_bound(x);
    if(it == begin(m)) return end(m);
    return prev(it);
}

template<typename K, typename V, typename Comp>
auto map_lt(const multimap<K,V,Comp>& m, const K& x) {
    auto it = m.lower_bound(x);
    if(it == begin(m)) return end(m);
    return prev(it);
}

template<typename K, typename V, typename Comp>
auto map_le(multimap<K,V,Comp>& m, const K& x) {
    auto it = m.upper_bound(x);
    if(it == begin(m)) return end(m);
    return prev(it);
}

template<typename K, typename V, typename Comp>
auto map_le(const multimap<K,V,Comp>& m, const K& x) {
    auto it = m.upper_bound(x);
    if(it == begin(m)) return end(m);
    return prev(it);
}

template<typename K, typename V, typename Comp>
auto map_gt(multimap<K,V,Comp>& m, const K& x) {
    return m.upper_bound(x);
}

template<typename K, typename V, typename Comp>
auto map_gt(const multimap<K,V,Comp>& m, const K& x) {
    return m.upper_bound(x);
}

template<typename K, typename V, typename Comp>
auto map_ge(multimap<K,V,Comp>& m, const K& x) {
    return m.lower_bound(x);
}

template<typename K, typename V, typename Comp>
auto map_ge(const multimap<K,V,Comp>& m, const K& x) {
    return m.lower_bound(x);
}
// }}}
// }}}

template<typename K, typename V, typename Comp>
bool map_contains(const map<K,V,Comp>& m, const typename map<K,V,Comp>::key_type& k) {
    return m.find(k) != end(m);
}

template<typename K, typename V, typename Hash, typename Eq>
bool map_contains(const unordered_map<K,V,Hash,Eq>& m, const typename unordered_map<K,V,Hash,Eq>::key_type& k) {
    return m.find(k) != end(m);
}

template<typename K, typename Comp>
bool multiset_erase_one(multiset<K,Comp>& m, const typename multiset<K,Comp>::key_type& k) {
    auto it = m.find(k);
    if(it == end(m)) return false;
    m.erase(it);
    return true;
}

template<typename K, typename Hash, typename Eq>
bool multiset_erase_one(unordered_multiset<K,Hash,Eq>& m, const typename unordered_multiset<K,Hash,Eq>::key_type& k) {
    auto it = m.find(k);
    if(it == end(m)) return false;
    m.erase(it);
    return true;
}

template<typename T>
using MaxHeap = priority_queue<T, vector<T>, less<T>>;
template<typename T>
using MinHeap = priority_queue<T, vector<T>, greater<T>>;

// POP() 系 {{{
// 効率は悪い
template<typename T>
T POP_FRONT(vector<T>& v) {
    T x = v.front(); v.erase(begin(v));
    return x;
}

template<typename T>
T POP_BACK(vector<T>& v) {
    T x = v.back(); v.pop_back();
    return x;
}

template<typename T>
T POP_FRONT(deque<T>& v) {
    T x = v.front(); v.pop_front();
    return x;
}

template<typename T>
T POP_BACK(deque<T>& v) {
    T x = v.back(); v.pop_back();
    return x;
}

template<typename T>
T POP_FRONT(forward_list<T>& ls) {
    T x = ls.front(); ls.pop_front();
    return x;
}

template<typename T>
T POP_FRONT(list<T>& ls) {
    T x = ls.front(); ls.pop_front();
    return x;
}

template<typename T>
T POP_BACK(list<T>& ls) {
    T x = ls.back(); ls.pop_back();
    return x;
}

template<typename T, typename C>
T POP(stack<T,C>& stk) {
    T x = stk.top(); stk.pop();
    return x;
}

template<typename T, typename C>
T POP(queue<T,C>& que) {
    T x = que.front(); que.pop();
    return x;
}

template<typename T, typename C, typename Comp>
T POP(priority_queue<T,C,Comp>& que) {
    T x = que.top(); que.pop();
    return x;
}
// }}}

// Formatter {{{
template<typename T, size_t N>
struct Formatter<array<T,N>> {
    static ostream& write_str(ostream& out, const array<T,N>& a) {
        return WRITE_RANGE_STR(out, begin(a), end(a));
    }
    static ostream& write_repr(ostream& out, const array<T,N>& a) {
        out << "array";
        return WRITE_RANGE_REPR(out, begin(a), end(a));
    }
};

template<typename T>
struct Formatter<deque<T>> {
    static ostream& write_str(ostream& out, const deque<T>& deq) {
        return WRITE_RANGE_STR(out, begin(deq), end(deq));
    }
    static ostream& write_repr(ostream& out, const deque<T>& deq) {
        out << "deque";
        return WRITE_RANGE_REPR(out, begin(deq), end(deq));
    }
};

template<typename T>
struct Formatter<forward_list<T>> {
    static ostream& write_str(ostream& out, const forward_list<T>& ls) {
        return WRITE_RANGE_STR(out, begin(ls), end(ls));
    }
    static ostream& write_repr(ostream& out, const forward_list<T>& ls) {
        out << "forward_list";
        return WRITE_RANGE_REPR(out, begin(ls), end(ls));
    }
};

template<typename T>
struct Formatter<list<T>> {
    static ostream& write_str(ostream& out, const list<T>& ls) {
        return WRITE_RANGE_STR(out, begin(ls), end(ls));
    }
    static ostream& write_repr(ostream& out, const list<T>& ls) {
        out << "list";
        return WRITE_RANGE_REPR(out, begin(ls), end(ls));
    }
};

template<typename T, typename Comp>
struct Formatter<set<T,Comp>> {
    static ostream& write_str(ostream& out, const set<T,Comp>& s) {
        return WRITE_RANGE_STR(out, begin(s), end(s));
    }
    static ostream& write_repr(ostream& out, const set<T,Comp>& s) {
        out << "set";
        return WRITE_RANGE_REPR(out, begin(s), end(s));
    }
};

template<typename T, typename Comp>
struct Formatter<multiset<T,Comp>> {
    static ostream& write_str(ostream& out, const multiset<T,Comp>& s) {
        return WRITE_RANGE_STR(out, begin(s), end(s));
    }
    static ostream& write_repr(ostream& out, const multiset<T,Comp>& s) {
        out << "multiset";
        return WRITE_RANGE_REPR(out, begin(s), end(s));
    }
};

template<typename T, typename Hash, typename Eq>
struct Formatter<unordered_set<T,Hash,Eq>> {
    static ostream& write_str(ostream& out, const unordered_set<T,Hash,Eq>& s) {
        return WRITE_RANGE_STR(out, begin(s), end(s));
    }
    static ostream& write_repr(ostream& out, const unordered_set<T,Hash,Eq>& s) {
        out << "unordered_set";
        return WRITE_RANGE_REPR(out, begin(s), end(s));
    }
};

template<typename T, typename Hash, typename Eq>
struct Formatter<unordered_multiset<T,Hash,Eq>> {
    static ostream& write_str(ostream& out, const unordered_multiset<T,Hash,Eq>& s) {
        return WRITE_RANGE_STR(out, begin(s), end(s));
    }
    static ostream& write_repr(ostream& out, const unordered_multiset<T,Hash,Eq>& s) {
        out << "unordered_multiset";
        return WRITE_RANGE_REPR(out, begin(s), end(s));
    }
};

template<typename K, typename V, typename Comp>
struct Formatter<map<K,V,Comp>> {
    static ostream& write_str(ostream& out, const map<K,V,Comp>& m) {
        return WRITE_RANGE_STR(out, begin(m), end(m));
    }
    static ostream& write_repr(ostream& out, const map<K,V,Comp>& m) {
        out << "map";
        return WRITE_RANGE_REPR(out, begin(m), end(m));
    }
};

template<typename K, typename V, typename Comp>
struct Formatter<multimap<K,V,Comp>> {
    static ostream& write_str(ostream& out, const multimap<K,V,Comp>& m) {
        return WRITE_RANGE_STR(out, begin(m), end(m));
    }
    static ostream& write_repr(ostream& out, const multimap<K,V,Comp>& m) {
        out << "multimap";
        return WRITE_RANGE_REPR(out, begin(m), end(m));
    }
};

template<typename K, typename V, typename Hash, typename Eq>
struct Formatter<unordered_map<K,V,Hash,Eq>> {
    static ostream& write_str(ostream& out, const unordered_map<K,V,Hash,Eq>& m) {
        return WRITE_RANGE_STR(out, begin(m), end(m));
    }
    static ostream& write_repr(ostream& out, const unordered_map<K,V,Hash,Eq>& m) {
        out << "unordered_map";
        return WRITE_RANGE_REPR(out, begin(m), end(m));
    }
};

template<typename K, typename V, typename Hash, typename Eq>
struct Formatter<unordered_multimap<K,V,Hash,Eq>> {
    static ostream& write_str(ostream& out, const unordered_multimap<K,V,Hash,Eq>& m) {
        return WRITE_RANGE_STR(out, begin(m), end(m));
    }
    static ostream& write_repr(ostream& out, const unordered_multimap<K,V,Hash,Eq>& m) {
        out << "unordered_multimap";
        return WRITE_RANGE_REPR(out, begin(m), end(m));
    }
};

template<typename T, typename C>
struct Formatter<stack<T,C>> {
    static ostream& write_str(ostream& out, const stack<T,C>& orig) {
        stack<T,C> stk(orig);
        while(!stk.empty()) {
            WRITE_STR(out, stk.top()); stk.pop();
            if(!stk.empty()) out << ' ';
        }
        return out;
    }
    static ostream& write_repr(ostream& out, const stack<T,C>& orig) {
        stack<T,C> stk(orig);
        out << "stack[";
        while(!stk.empty()) {
            WRITE_REPR(out, stk.top()); stk.pop();
            if(!stk.empty()) out << ", ";
        }
        out << "]";
        return out;
    }
};

template<typename T, typename C>
struct Formatter<queue<T,C>> {
    static ostream& write_str(ostream& out, const queue<T,C>& orig) {
        queue<T,C> que(orig);
        while(!que.empty()) {
            WRITE_STR(out, que.front()); que.pop();
            if(!que.empty()) out << ' ';
        }
        return out;
    }
    static ostream& write_repr(ostream& out, const queue<T,C>& orig) {
        queue<T,C> que(orig);
        out << "queue[";
        while(!que.empty()) {
            WRITE_REPR(out, que.front()); que.pop();
            if(!que.empty()) out << ", ";
        }
        out << "]";
        return out;
    }
};

template<typename T, typename C, typename Comp>
struct Formatter<priority_queue<T,C,Comp>> {
    static ostream& write_str(ostream& out, const priority_queue<T,C,Comp>& orig) {
        priority_queue<T,C,Comp> que(orig);
        while(!que.empty()) {
            WRITE_STR(out, que.top()); que.pop();
            if(!que.empty()) out << ' ';
        }
        return out;
    }
    static ostream& write_repr(ostream& out, const priority_queue<T,C,Comp>& orig) {
        priority_queue<T,C,Comp> que(orig);
        out << "priority_queue[";
        while(!que.empty()) {
            WRITE_REPR(out, que.top()); que.pop();
            if(!que.empty()) out << ", ";
        }
        out << "]";
        return out;
    }
};

template<>
struct Formatter<BoolArray> {
    static ostream& write_str(ostream& out, const BoolArray& a) {
        return WRITE_RANGE_STR(out, begin(a), end(a));
    }
    static ostream& write_repr(ostream& out, const BoolArray& a) {
        out << "BoolArray";
        return WRITE_RANGE_REPR(out, begin(a), end(a));
    }
};
// }}}

// }}}

// grid (container が必要) {{{

struct Index2 {
    i64 y, x;

    Index2(i64 yy, i64 xx) : y(yy), x(xx) {}
    explicit Index2(const pair<i64,i64>& p) : Index2(p.first,p.second) {}

    Index2 operator-() const {
        return Index2(-y,-x);
    }
    Index2& operator+=(const Index2& rhs) {
        y += rhs.y;
        x += rhs.x;
        return *this;
    }
    Index2& operator-=(const Index2& rhs) {
        y -= rhs.y;
        x -= rhs.x;
        return *this;
    }
    Index2& operator*=(i64 rhs) {
        y *= rhs;
        x *= rhs;
        return *this;
    }
    Index2& operator/=(i64 rhs) {
        y /= rhs;
        x /= rhs;
        return *this;
    }

    i64 norm1() const { return abs(y) + abs(x); }

    vector<Index2> neighbor4() const {
        return {
            { y-1, x   },
            { y  , x-1 },
            { y  , x+1 },
            { y+1, x   },
        };
    }
    vector<Index2> neighbor8() const {
        return {
            { y-1, x-1 },
            { y-1, x   },
            { y-1, x+1 },
            { y  , x-1 },
            { y  , x+1 },
            { y+1, x-1 },
            { y+1, x   },
            { y+1, x+1 },
        };
    }
};

Index2 operator+(const Index2& lhs, const Index2& rhs) { return Index2(lhs) += rhs; }
Index2 operator-(const Index2& lhs, const Index2& rhs) { return Index2(lhs) -= rhs; }
Index2 operator*(const Index2& lhs, i64 rhs) { return Index2(lhs) *= rhs; }
Index2 operator*(i64 lhs, const Index2& rhs) { return Index2(rhs) *= lhs; }
Index2 operator/(const Index2& lhs, i64 rhs) { return Index2(lhs) /= rhs; }

bool operator==(const Index2& lhs, const Index2& rhs) {
    return lhs.y == rhs.y && lhs.x == rhs.x;
}

template<>
struct Formatter<Index2> {
    static ostream& write_str(ostream& out, const Index2& idx) {
        WRITE_STR(out, idx.y);
        out << ' ';
        WRITE_STR(out, idx.x);
        return out;
    }
    static ostream& write_repr(ostream& out, const Index2& idx) {
        out << "(";
        WRITE_REPR(out, idx.y);
        out << ",";
        WRITE_REPR(out, idx.x);
        out << ")";
        return out;
    }
};

template<typename T>
struct Grid2Container {
    using inner = vector<T>;
    using outer = vector<inner>;
};
template<>
struct Grid2Container<bool> {
    using inner = BoolArray;
    using outer = vector<inner>;
};

template<typename T>
struct Grid2 {
    using inner = typename Grid2Container<T>::inner;
    using outer = typename Grid2Container<T>::outer;

    outer cont_;

    Grid2(i64 h, i64 w, const T& val) : cont_(h, inner(w,val)) {
        assert(h >= 1);
        assert(w >= 1);
    }
    Grid2(i64 h, i64 w) : Grid2(h, w, T()) {}

    i64 h() const { return SIZE(cont_);    }
    i64 w() const { return SIZE(cont_[0]); }

          T& operator[](const Index2& idx)       { return at(idx.y, idx.x); }
    const T& operator[](const Index2& idx) const { return at(idx.y, idx.x); }

          T& at(i64 y, i64 x)       { return cont_[y][x]; }
    const T& at(i64 y, i64 x) const { return cont_[y][x]; }

    bool idx_is_valid(const Index2& idx) const { return idx_is_valid(idx.y, idx.x); }
    bool idx_is_valid(i64 y, i64 x) const {
        return 0 <= y && y < h() && 0 <= x && x < w();
    }

    vector<Index2> neighbor4(const Index2& idx) const {
        vector<Index2> res = idx.neighbor4();
        auto it = ALL(remove_if, res, [this](const auto& to) { return !this->idx_is_valid(to); });
        res.erase(it, end(res));
        return res;
    }
    vector<Index2> neighbor4(i64 y, i64 x) const { return neighbor4({y,x}); }

    vector<Index2> neighbor8(const Index2& idx) const {
        vector<Index2> res = idx.neighbor8();
        auto it = ALL(remove_if, res, [this](const auto& to) { return !this->idx_is_valid(to); });
        res.erase(it, end(res));
        return res;
    }
    vector<Index2> neighbor8(i64 y, i64 x) const { return neighbor8({y,x}); }
};

template<typename T>
struct Formatter<Grid2<T>> {
    static ostream& write_str(ostream& out, const Grid2<T>& grid) {
        return write_repr(out, grid);
    }
    static ostream& write_repr(ostream& out, const Grid2<T>& grid) {
        out << "\n";
        for(const auto& row : grid.cont_) {
            WRITE_STR(out, row);
            out << "\n";
        }
        out << "\n";
        return out;
    }
};

template<>
struct Formatter<Grid2<char>> {
    static ostream& write_str(ostream& out, const Grid2<char>& grid) {
        return write_repr(out, grid);
    }
    static ostream& write_repr(ostream& out, const Grid2<char>& grid) {
        out << "\n";
        for(const auto& row : grid.cont_) {
            ALL(copy, row, ostream_iterator<char>(out));
            out << "\n";
        }
        out << "\n";
        return out;
    }
};

// }}}

//--------------------------------------------------------------------



void solve() {
    i64 H,W; RD(H); RD(W);

    Grid2<i64> grid(H, W);
    REP(y, H) REP(x, W) {
        RD(grid.at(y,x));
    }

    auto dfs = FIX([&grid](auto self, const Index2& idx) -> void {
        grid[idx] = 0;
        for(const auto& to : grid.neighbor4(idx)) {
            if(grid[to] == 1)
                self(to);
        }
    });

    i64 ans = 0;
    REP(y, H) REP(x, W) {
        if(grid.at(y,x) == 1) {
            ++ans;
            dfs(Index2(y,x));
            DBG(grid);
        }
    }

    // * 無効値 INF をそのまま出力してない?
    // * MOD はとった?
    // * 入出力の 0-based/1-based 確認した?
    // * 時間/メモリ制限は確認した?
    // * 違うやつ提出してない?
    // * 違うやつテストしてない?
    PRINTLN(ans);
}

signed main() {
    

    solve();

    EXIT();
}