#pragma region Macros #pragma comment(linker, "/stack:200000000") // #pragma GCC optimize("unroll-loops") // #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,fma,abm,mmx,avx,avx2,tune=native") // #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,fma,abm,mmx,avx,avx2") // #pragma GCC target("avx2") #pragma GCC optimize("Ofast") #include #define ll long long using ld = long double; #define rep2(i, a, b) for(ll i = (a); i <= (b); i++) #define rep3(i, a, b) for(ll i = (a); i >= (b); --i) #define rep(i, n) for(ll i = 0; i < n; ++i) #define each(i, a) for(auto &i : a) #define pii pair #define pll pair #define pb push_back #define eb emplace_back #define vi vector #define vll vector #define vpi vector #define vpll vector #define overload2(_1, _2, name, ...) name #define vec(type, name, ...) vector name(__VA_ARGS__) #define VEC(type, name, size) \ vector name(size); \ IN(name) #define VEC2(type, name1, name2, size) \ vector name1(size), name2(size); \ for(int i = 0; i < size; i++) IN(name1[i], name2[i]) #define VEC3(type, name1, name2, name3, size) \ vector name1(size), name2(size), name3(size); \ for(int i = 0; i < size; i++) IN(name1[i], name2[i], name3[i]) #define vv(type, name, h, ...) vector> name(h, vector(__VA_ARGS__)) #define VV(type, name, h, w) \ vector> name(h, vector(w)); \ IN(name) #define vvv(type, name, h, w, ...) vector>> name(h, vector>(w, vector(__VA_ARGS__))) #define vvvv(type, name, a, b, c, ...) \ vector>>> name(a, vector>>(b, vector>(c, vector(__VA_ARGS__)))) #define mt make_tuple #define fi first #define se second #define all(c) begin(c), end(c) #define rall(c) rbegin(c), rend(c) #define SORT(v) sort(all(v)) #define REV(v) reverse(all(v)) template T SUM(const S &v) { return accumulate(all(v), T(0)); } #define MIN(v) *min_element(all(v)) #define MAX(v) *max_element(all(v)) #define lb(c, x) distance((c).begin(), lower_bound(all(c), (x))) #define ub(c, x) distance((c).begin(), upper_bound(all(c), (x))) using namespace std; constexpr pii dx4[4] = {pii{1, 0}, pii{0, 1}, pii{-1, 0}, pii{0, -1}}; constexpr pii dx8[8] = {{1, 0}, {1, 1}, {0, 1}, {-1, 1}, {-1, 0}, {-1, -1}, {0, -1}, {1, -1}}; const string YESNO[2] = {"NO", "YES"}; const string YesNo[2] = {"No", "Yes"}; const string yesno[2] = {"no", "yes"}; void YES(bool t = 1) { cout << YESNO[t] << endl; } void NO(bool t = 1) { YES(!t); } void Yes(bool t = 1) { cout << YesNo[t] << endl; } void No(bool t = 1) { Yes(!t); } void yes(bool t = 1) { cout << yesno[t] << endl; } void no(bool t = 1) { yes(!t); } template using vc = vector; template using vvc = vector>; template using vvvc = vector>; template using vvvvc = vector>; template using pq = priority_queue; template using pqg = priority_queue, greater>; #define si(c) (int)(c).size() #define INT(...) \ int __VA_ARGS__; \ IN(__VA_ARGS__) #define LL(...) \ ll __VA_ARGS__; \ IN(__VA_ARGS__) #define STR(...) \ string __VA_ARGS__; \ IN(__VA_ARGS__) #define CHR(...) \ char __VA_ARGS__; \ IN(__VA_ARGS__) #define DBL(...) \ double __VA_ARGS__; \ IN(__VA_ARGS__) int scan() { return getchar(); } void scan(int &a) { cin >> a; } void scan(long long &a) { cin >> a; } void scan(char &a) { cin >> a; } void scan(double &a) { cin >> a; } void scan(string &a) { cin >> a; } template void scan(pair &p) { scan(p.first), scan(p.second); } template void scan(vector &); template void scan(vector &a) { for(auto &i : a) scan(i); } template void scan(T &a) { cin >> a; } void IN() {} template void IN(Head &head, Tail &...tail) { scan(head); IN(tail...); } template inline bool chmax(T &a, const S &b) { return (a < b ? a = b, 1 : 0); } template inline bool chmin(T &a, const S &b) { return (a > b ? a = b, 1 : 0); } vi iota(int n) { vi a(n); iota(all(a), 0); return a; } template vi iota(vector &a, bool greater = false) { vi res(a.size()); iota(all(res), 0); sort(all(res), [&](int i, int j) { if(greater) return a[i] > a[j]; return a[i] < a[j]; }); return res; } #define UNIQUE(x) sort(all(x)), x.erase(unique(all(x)), x.end()) template T ceil(T x, T y) { assert(y >= 1); return (x > 0 ? (x + y - 1) / y : x / y); } template T floor(T x, T y) { assert(y >= 1); return (x > 0 ? x / y : (x + y - 1) / y); } template T POW(T x, int n) { T res = 1; for(; n; n >>= 1, x *= x) if(n & 1) res *= x; return res; } template T POW(T x, ll n, const ll &mod) { T res = 1; for(; n; n >>= 1, x = x * x % mod) if(n & 1) res = res * x % mod; return res; } vector factor(ll x) { vector ans; for(ll i = 2; i * i <= x; i++) if(x % i == 0) { ans.push_back({i, 1}); while((x /= i) % i == 0) ans.back().second++; } if(x != 1) ans.push_back({x, 1}); return ans; } template vector divisor(T x) { vector ans; for(T i = 1; i * i <= x; i++) if(x % i == 0) { ans.pb(i); if(i * i != x) ans.pb(x / i); } return ans; } template void zip(vector &x) { vector y = x; UNIQUE(y); for(int i = 0; i < x.size(); ++i) { x[i] = lb(y, x[i]); } } template void fold_in(vector &v) {} template void fold_in(vector &v, Head &&a, Tail &&...tail) { for(auto e : a) v.emplace_back(e); fold_in(v, tail...); } template void renumber(vector &v) {} template void renumber(vector &v, Head &&a, Tail &&...tail) { for(auto &&e : a) e = lb(v, e); renumber(v, tail...); } template vector zip(vector &head, Args &&...args) { vector v; fold_in(v, head, args...); sort(all(v)), v.erase(unique(all(v)), v.end()); renumber(v, head, args...); return v; } // x in [l, r) template bool inc(const T &x, const S &l, const S &r) { return l <= x and x < r; } // (a, b) in [lx, rx) * [ly, ry) template bool inc(const pair &x, const S &lx, const S &ly, const S &rx, const S &ry) { return inc(x.fi, lx, rx) && inc(x.se, ly, ry); } constexpr ll ten(int n) { return n == 0 ? 1 : ten(n - 1) * 10; } // bit 演算系 ll pow2(int i) { return 1LL << i; } int topbit(signed t) { return t == 0 ? -1 : 31 - __builtin_clz(t); } int topbit(ll t) { return t == 0 ? -1 : 63 - __builtin_clzll(t); } int lowbit(signed a) { return a == 0 ? 32 : __builtin_ctz(a); } int lowbit(ll a) { return a == 0 ? 64 : __builtin_ctzll(a); } // int allbit(int n) { return (1 << n) - 1; } ll allbit(ll n) { return (1LL << n) - 1; } int popcount(signed t) { return __builtin_popcount(t); } int popcount(ll t) { return __builtin_popcountll(t); } bool ispow2(int i) { return i && (i & -i) == i; } ll rnd(ll l, ll r) { //[l, r) #ifdef _LOCAL static mt19937_64 gen; #else static mt19937_64 gen(chrono::steady_clock::now().time_since_epoch().count()); #endif return uniform_int_distribution(l, r - 1)(gen); } ll rnd(ll n) { return rnd(0, n); } template void random_shuffle(vc &a) { rep(i, si(a)) swap(a[i], a[rnd(0, i)]); } int in() { int x; cin >> x; return x; } ll lin() { unsigned long long x; cin >> x; return x; } template pair operator-(const pair &x, const pair &y) { return pair(x.fi - y.fi, x.se - y.se); } template pair operator+(const pair &x, const pair &y) { return pair(x.fi + y.fi, x.se + y.se); } template pair operator&(const pair &l, const pair &r) { return pair(max(l.fi, r.fi), min(l.se, r.se)); } template pair operator+=(pair &l, const pair &r) { return l = l + r; } template pair operator-=(pair &l, const pair &r) { return l = l - r; } template bool intersect(const pair &l, const pair &r) { return (l.se < r.se ? r.fi < l.se : l.fi < r.se); } template ll operator*(const pair &x, const pair &y) { return (ll)x.fi * y.fi + (ll)x.se * y.se; } template struct edge { int from, to; T cost; int id; edge(int to, T cost) : from(-1), to(to), cost(cost) {} edge(int from, int to, T cost) : from(from), to(to), cost(cost) {} edge(int from, int to, T cost, int id) : from(from), to(to), cost(cost), id(id) {} constexpr bool operator<(const edge &rhs) const noexcept { return cost < rhs.cost; } edge &operator=(const int &x) { to = x; return *this; } operator int() const { return to; } }; template using Edges = vector>; using Tree = vector>; using Graph = vector>; template using Wgraph = vector>>; Graph getG(int n, int m = -1, bool directed = false, int margin = 1) { Tree res(n); if(m == -1) m = n - 1; while(m--) { int a, b; cin >> a >> b; a -= margin, b -= margin; res[a].emplace_back(b); if(!directed) res[b].emplace_back(a); } return res; } Graph getTreeFromPar(int n, int margin = 1) { Graph res(n); for(int i = 1; i < n; i++) { int a; cin >> a; res[a - margin].emplace_back(i); } return res; } template Wgraph getWg(int n, int m = -1, bool directed = false, int margin = 1) { Wgraph res(n); if(m == -1) m = n - 1; while(m--) { int a, b; T c; cin >> a >> b >> c; a -= margin, b -= margin; res[a].emplace_back(b, c); if(!directed) res[b].emplace_back(a, c); } return res; } void add(Graph &G, int x, int y) { G[x].eb(y), G[y].eb(x); } template void add(Wgraph &G, int x, int y, S c) { G[x].eb(y, c), G[y].eb(x, c); } #define i128 __int128_t #define ull unsigned long long int #define TEST \ INT(testcases); \ while(testcases--) template ostream &operator<<(ostream &os, const vector &v) { for(auto it = begin(v); it != end(v); ++it) { if(it == begin(v)) os << *it; else os << " " << *it; } return os; } template ostream &operator<<(ostream &os, const pair &p) { os << p.first << " " << p.second; return os; } template string to_string(pair p) { return "(" + to_string(p.first) + "," + to_string(p.second) + ")"; } string to_string(string s) { return "\"" + s + "\""; } string to_string(char c) { return string(1, c); } template string to_string(vector s) { string res = "{"; for(auto it = s.begin(); it != s.end(); it++) res += to_string(*it) + (next(it) == s.end() ? "" : ", "); return res + "}"; } template string to_string(set s) { string res = "{"; for(auto it = s.begin(); it != s.end(); it++) res += to_string(*it), res += (next(it) == end(s) ? "" : ", "); return res + "}"; } #define endl '\n' #ifdef _LOCAL void dump() { cerr << endl; } template void dump(Head head, Tail... tail) { cerr << to_string(head) << " "; dump(tail...); } #undef endl #define debug(x) \ cout << #x << ": "; \ dump(x) #else void dump() {} template void dump(Head head, Tail... tail) {} #define debug(x) #endif template void print(const T &a) { cout << a; } void OUT() { cout << endl; } template void OUT(const Head &head, const Tail &...tail) { print(head); if(sizeof...(tail)) cout << ' '; OUT(tail...); } template static constexpr T inf = numeric_limits::max() / 2; struct Setup_io { Setup_io() { ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0); cout << fixed << setprecision(15); } } setup_io; #define drop(s) cout << #s << endl, exit(0) template struct ndFORarray { std::array v; ndFORarray(std::array v_) : v(v_) {} struct ndFORitr { const std::array &v; std::array tmp; bool is_end; ndFORitr(const std::array &v_) : v(v_), tmp(), is_end(false) {} bool operator!=(const ndFORitr &) const { return !is_end; } void operator++() { int pos = N - 1; while(pos != -1) { tmp[pos] += 1; if(tmp[pos] == v[pos]) { tmp[pos] = 0; pos -= 1; } else { break; } } if(pos == -1) { is_end = true; } } const std::array &operator*() const { return tmp; } }; ndFORitr begin() const { return ndFORitr(v); } ndFORitr end() const { return ndFORitr(v); } }; struct ndFORvector { std::vector v; ndFORvector(std::vector v_) : v(v_) {} struct ndFORitr { const std::vector &v; std::vector tmp; bool is_end; ndFORitr(const std::vector &v_) : v(v_), tmp(v.size(), 0), is_end(false) {} bool operator!=(const ndFORitr &) const { return !is_end; } void operator++() { int pos = v.size() - 1; while(pos != -1) { tmp[pos] += 1; if(tmp[pos] == v[pos]) { tmp[pos] = 0; pos -= 1; } else { break; } } if(pos == -1) { is_end = true; } } const std::vector &operator*() const { return tmp; } }; ndFORitr begin() const { return ndFORitr(v); } ndFORitr end() const { return ndFORitr(v); } }; auto ndFOR(std::vector v) { return ndFORvector(v); } template auto ndFOR(Ts... v) { return ndFORarray>::value>({v...}); } template struct REC { F f; REC(F &&f_) : f(std::forward(f_)) {} template auto operator()(Args &&...args) const { return f(*this, std::forward(args)...); } }; template vector> runLength(const vector &v) { vector> res; for(auto &e : v) { if(res.empty() or res.back().fi != e) res.eb(e, 1); else res.back().se++; } return res; } vector> runLength(const string &v) { vector> res; for(auto &e : v) { if(res.empty() or res.back().fi != e) res.eb(e, 1); else res.back().se++; } return res; } template struct Imos { int n; vector a; Imos(int _n) : n(_n), a(_n + 1) {} void add(int l, int r, T val = 1) { if(l >= r) return; l = clamp(l, 0, n); r = clamp(r, 0, n + 1); a[l] += val; if(r <= n) a[r] -= val; } void build() { for(int i = 0; i < n; i++) a[i + 1] += a[i]; } const T &operator[](int k) { return a[k]; } }; template T bin_search(T ok, T ng, const F &f) { while(abs(ok - ng) > 1) { T mid = ok + ng >> 1; (f(mid) ? ok : ng) = mid; } return ok; } #pragma endregion const int MAX_ROW = 5100; // to be set appropriately const int MAX_COL = 5100; // to be set appropriately struct BitMatrix { int H, W; bitset val[MAX_ROW]; BitMatrix(int m = 1, int n = 1) : H(m), W(n) {} inline bitset &operator[](int i) { return val[i]; } }; int GaussJordan(BitMatrix &A, bool is_extended = false) { int rank = 0; for(int col = 0; col < A.W; ++col) { if(is_extended && col == A.W - 1) break; int pivot = -1; for(int row = rank; row < A.H; ++row) { if(A[row][col]) { pivot = row; break; } } if(pivot == -1) continue; swap(A[pivot], A[rank]); for(int row = 0; row < A.H; ++row) { if(row != rank && A[row][col]) A[row] ^= A[rank]; } ++rank; } return rank; } int linear_equation(BitMatrix A, vector b, vector &res) { int m = A.H, n = A.W; BitMatrix M(m, n + 1); for(int i = 0; i < m; ++i) { for(int j = 0; j < n; ++j) M[i][j] = A[i][j]; M[i][n] = b[i]; } int rank = GaussJordan(M, true); // check if it has no solution for(int row = rank; row < m; ++row) if(M[row][n]) return -1; // answer res.assign(n, 0); for(int i = 0; i < rank; ++i) res[i] = M[i][n]; return rank; } int main() { INT(n, m); BitMatrix bm(n, n); rep(i, m) { INT(r, c); r--, c--; bm[r][c] = 1; } bool flag = true; rep(i, n) { bool fl = true; rep(j, n) fl &= bm[i][j] == bm[i][0]; flag &= fl; } if(flag) drop(0); flag = true; rep(j, n) { bool fl = true; rep(i, n) fl &= bm[i][j] == bm[0][j]; flag &= fl; } if(flag) drop(0); OUT(GaussJordan(bm) + 1); }