#line 1 "/home/maspy/compro/library/my_template.hpp" #include using namespace std; using ll = long long; using pi = pair; using vi = vector; using u32 = unsigned int; using u64 = unsigned long long; using i128 = __int128; template using vc = vector; template using vvc = vector>; template using vvvc = vector>; template using vvvvc = vector>; template using vvvvvc = vector>; template using pq = priority_queue; template using pqg = priority_queue, greater>; #define vec(type, name, ...) vector name(__VA_ARGS__) #define vv(type, name, h, ...) \ vector> name(h, vector(__VA_ARGS__)) #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 FOR_(n) for (ll _ = 0; (_) < (ll)(n); ++(_)) #define FOR(i, n) for (ll i = 0; (i) < (ll)(n); ++(i)) #define FOR3(i, m, n) for (ll i = (m); (i) < (ll)(n); ++(i)) #define FOR_R(i, n) for (ll i = (ll)(n)-1; (i) >= 0; --(i)) #define FOR3_R(i, m, n) for (ll i = (ll)(n)-1; (i) >= (ll)(m); --(i)) #define FOR_subset(t, s) for (ll t = s; t >= 0; t = (t == 0 ? -1 : (t - 1) & s)) #define all(x) x.begin(), x.end() #define len(x) ll(x.size()) #define elif else if #define eb emplace_back #define mp make_pair #define mt make_tuple #define fi first #define se second #define stoi stoll template T SUM(vector &A) { T sum = T(0); for (auto &&a: A) sum += a; return sum; } #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))) #define UNIQUE(x) sort(all(x)), x.erase(unique(all(x)), x.end()) int popcnt(int x) { return __builtin_popcount(x); } int popcnt(u32 x) { return __builtin_popcount(x); } int popcnt(ll x) { return __builtin_popcountll(x); } int popcnt(u64 x) { return __builtin_popcountll(x); } // (0, 1, 2, 3, 4) -> (-1, 0, 1, 1, 2) int topbit(int x) { return (x == 0 ? -1 : 31 - __builtin_clz(x)); } int topbit(u32 x) { return (x == 0 ? -1 : 31 - __builtin_clz(x)); } int topbit(ll x) { return (x == 0 ? -1 : 63 - __builtin_clzll(x)); } int topbit(u64 x) { return (x == 0 ? -1 : 63 - __builtin_clzll(x)); } // (0, 1, 2, 3, 4) -> (-1, 0, 1, 0, 2) int lowbit(int x) { return (x == 0 ? -1 : 31 - __builtin_clz(x)); } int lowbit(u32 x) { return (x == 0 ? -1 : 31 - __builtin_clz(x)); } int lowbit(ll x) { return (x == 0 ? -1 : 63 - __builtin_clzll(x)); } int lowbit(u64 x) { return (x == 0 ? -1 : 63 - __builtin_clzll(x)); } template T ceil(T x, U y) { return (x > 0 ? (x + y - 1) / y : x / y); } template T floor(T x, U y) { return (x > 0 ? x / y : (x - y + 1) / y); } template pair divmod(T x, U y) { T q = floor(x, y); return {q, x - q * y}; } ll binary_search(function check, ll ok, ll ng) { assert(check(ok)); while (abs(ok - ng) > 1) { auto x = (ng + ok) / 2; if (check(x)) ok = x; else ng = x; } return ok; } 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 s_to_vi(const string& S, char first_char) { vi A(S.size()); FOR(i, S.size()) { A[i] = S[i] - first_char; } return A; } template vector cumsum(vector &A, int off = 1) { int N = A.size(); vector B(N + 1); FOR(i, N) { B[i + 1] = B[i] + A[i]; } if (off == 0) B.erase(B.begin()); return B; } template vc bincount(const vc &A, int size) { vc C(size); for (auto &&x: A) { ++C[x]; } return C; } template vector argsort(const vector &A) { // stable vector ids(A.size()); iota(all(ids), 0); sort(all(ids), [&](int i, int j) { return A[i] < A[j] || (A[i] == A[j] && i < j); }); return ids; } // A[I[0]], A[I[1]], ... template vc rearrange(const vc &A, const vc &I) { int n = len(A); assert(len(I) == n); vc B(n); FOR(i, n) B[i] = A[I[i]]; return B; } #line 1 "/home/maspy/compro/library/other/io.hpp" // based on yosupo's fastio #include namespace detail { template std::true_type check_value(int); template std::false_type check_value(long); } // namespace detail template struct is_modint : decltype(detail::check_value(0)) {}; template using is_modint_t = enable_if_t::value>; template using is_not_modint_t = enable_if_t::value>; struct Scanner { FILE *fp; char line[(1 << 15) + 1]; size_t st = 0, ed = 0; void reread() { memmove(line, line + st, ed - st); ed -= st; st = 0; ed += fread(line + ed, 1, (1 << 15) - ed, fp); line[ed] = '\0'; } bool succ() { while (true) { if (st == ed) { reread(); if (st == ed) return false; } while (st != ed && isspace(line[st])) st++; if (st != ed) break; } if (ed - st <= 50) { bool sep = false; for (size_t i = st; i < ed; i++) { if (isspace(line[i])) { sep = true; break; } } if (!sep) reread(); } return true; } template ::value, int> = 0> bool read_single(T &ref) { if (!succ()) return false; while (true) { size_t sz = 0; while (st + sz < ed && !isspace(line[st + sz])) sz++; ref.append(line + st, sz); st += sz; if (!sz || st != ed) break; reread(); } return true; } template ::value, int> = 0> bool read_single(T &ref) { if (!succ()) return false; bool neg = false; if (line[st] == '-') { neg = true; st++; } ref = T(0); while (isdigit(line[st])) { ref = 10 * ref + (line[st++] & 0xf); } if (neg) ref = -ref; return true; } template * = nullptr> bool read_single(T &ref) { long long val = 0; bool f = read_single(val); ref = T(val); return f; } bool read_single(double &ref) { string s; if (!read_single(s)) return false; ref = std::stod(s); return true; } bool read_single(char &ref) { string s; if (!read_single(s) || s.size() != 1) return false; ref = s[0]; return true; } template bool read_single(vector &ref) { for (auto &d: ref) { if (!read_single(d)) return false; } return true; } template bool read_single(pair &p) { return (read_single(p.first) && read_single(p.second)); } template bool read_single(tuple &p) { return (read_single(get<0>(p)) && read_single(get<1>(p)) && read_single(get<2>(p))); } template bool read_single(tuple &p) { return (read_single(get<0>(p)) && read_single(get<1>(p)) && read_single(get<2>(p)) && read_single(get<3>(p))); } void read() {} template void read(H &h, T &... t) { bool f = read_single(h); assert(f); read(t...); } Scanner(FILE *fp) : fp(fp) {} }; struct Printer { Printer(FILE *_fp) : fp(_fp) {} ~Printer() { flush(); } static constexpr size_t SIZE = 1 << 15; FILE *fp; char line[SIZE], small[50]; size_t pos = 0; void flush() { fwrite(line, 1, pos, fp); pos = 0; } void write(const char &val) { if (pos == SIZE) flush(); line[pos++] = val; } template ::value, int> = 0> void write(T val) { if (pos > (1 << 15) - 50) flush(); if (val == 0) { write('0'); return; } if (val < 0) { write('-'); val = -val; // todo min } size_t len = 0; while (val) { small[len++] = char(0x30 | (val % 10)); val /= 10; } for (size_t i = 0; i < len; i++) { line[pos + i] = small[len - 1 - i]; } pos += len; } void write(const string &s) { for (char c: s) write(c); } void write(const char *s) { size_t len = strlen(s); for (size_t i = 0; i < len; i++) write(s[i]); } void write(const double &x) { ostringstream oss; oss << setprecision(15) << x; string s = oss.str(); write(s); } void write(const long double &x) { ostringstream oss; oss << setprecision(15) << x; string s = oss.str(); write(s); } template * = nullptr> void write(T &ref) { write(ref.val); } template void write(const vector &val) { auto n = val.size(); for (size_t i = 0; i < n; i++) { if (i) write(' '); write(val[i]); } } template void write(const pair &val) { write(val.first); write(' '); write(val.second); } template void write(const tuple &val) { auto &[a, b, c] = val; write(a), write(' '), write(b), write(' '), write(c); } template void write(const tuple &val) { auto &[a, b, c, d] = val; write(a), write(' '), write(b), write(' '), write(c), write(' '), write(d); } template void write(const tuple &val) { auto &[a, b, c, d, e] = val; write(a), write(' '), write(b), write(' '), write(c), write(' '), write(d), write(' '), write(e); } template void write(const tuple &val) { auto &[a, b, c, d, e, f] = val; write(a), write(' '), write(b), write(' '), write(c), write(' '), write(d), write(' '), write(e), write(' '), write(f); } template void write(const array &val) { auto n = val.size(); for (size_t i = 0; i < n; i++) { if (i) write(' '); write(val[i]); } } void write(i128 val) { string s; bool negative = 0; if(val < 0){ negative = 1; val = -val; } while (val) { s += '0' + int(val % 10); val /= 10; } if(negative) s += "-"; reverse(all(s)); if (len(s) == 0) s = "0"; write(s); } }; Scanner scanner = Scanner(stdin); Printer printer = Printer(stdout); void flush() { printer.flush(); } void print() { printer.write('\n'); } template void print(Head &&head, Tail &&... tail) { printer.write(head); if (sizeof...(Tail)) printer.write(' '); print(forward(tail)...); } void read() {} template void read(Head &head, Tail &... tail) { scanner.read(head); read(tail...); } #define INT(...) \ int __VA_ARGS__; \ read(__VA_ARGS__) #define LL(...) \ ll __VA_ARGS__; \ read(__VA_ARGS__) #define STR(...) \ string __VA_ARGS__; \ read(__VA_ARGS__) #define CHAR(...) \ char __VA_ARGS__; \ read(__VA_ARGS__) #define DBL(...) \ double __VA_ARGS__; \ read(__VA_ARGS__) #define VEC(type, name, size) \ vector name(size); \ read(name) #define VV(type, name, h, w) \ vector> name(h, vector(w)); \ read(name) void YES(bool t = 1) { print(t ? "YES" : "NO"); } void NO(bool t = 1) { YES(!t); } void Yes(bool t = 1) { print(t ? "Yes" : "No"); } void No(bool t = 1) { Yes(!t); } void yes(bool t = 1) { print(t ? "yes" : "no"); } void no(bool t = 1) { yes(!t); } #line 2 "/home/maspy/compro/library/ds/segtree.hpp" template struct SegTree { using X = typename Monoid::value_type; using value_type = X; vc dat; int n, log, size; SegTree() : SegTree(0) {} SegTree(int n) : SegTree(vc(n, Monoid::unit())) {} SegTree(vc v) : n(len(v)) { log = 1; while ((1 << log) < n) ++log; size = 1 << log; dat.assign(size << 1, Monoid::unit()); FOR(i, n) dat[size + i] = v[i]; FOR3_R(i, 1, size) update(i); } X operator[](int i) { return dat[size + i]; } void update(int i) { dat[i] = Monoid::op(dat[2 * i], dat[2 * i + 1]); } void set(int i, X x) { assert(i < n); dat[i += size] = x; while (i >>= 1) update(i); } X prod(int L, int R) { assert(L <= R); assert(R <= n); X vl = Monoid::unit(), vr = Monoid::unit(); L += size, R += size; while (L < R) { if (L & 1) vl = Monoid::op(vl, dat[L++]); if (R & 1) vr = Monoid::op(dat[--R], vr); L >>= 1, R >>= 1; } return Monoid::op(vl, vr); } X prod_all() { return dat[1]; } template int max_right(F &check, int L) { assert(0 <= L && L <= n && check(Monoid::unit())); if (L == n) return n; L += size; X sm = Monoid::unit(); do { while (L % 2 == 0) L >>= 1; if (!check(Monoid::op(sm, dat[L]))) { while (L < size) { L = 2 * L; if (check(Monoid::op(sm, dat[L]))) { sm = Monoid::op(sm, dat[L]); L++; } } return L - size; } sm = Monoid::op(sm, dat[L]); L++; } while ((L & -L) != L); return n; } template int min_left(F &check, int R) { assert(0 <= R && R <= n && check(Monoid::unit())); if (R == 0) return 0; R += size; X sm = Monoid::unit(); do { --R; while (R > 1 && (R % 2)) R >>= 1; if (!check(Monoid::op(dat[R], sm))) { while (R < size) { R = 2 * R + 1; if (check(Monoid::op(dat[R], sm))) { sm = Monoid::op(dat[R], sm); R--; } } return R + 1 - size; } sm = Monoid::op(dat[R], sm); } while ((R & -R) != R); return 0; } // モノイドが可換なら、prod_{l<=i= r) break; if (l & 1) { x = Monoid::op(x, dat[(size >> k) + ((l++) ^ xor_val)]); } if (r & 1) { x = Monoid::op(x, dat[(size >> k) + ((--r) ^ xor_val)]); } l /= 2, r /= 2, xor_val /= 2; } return x; } void debug() { print("segtree", dat); } }; #line 2 "/home/maspy/compro/library/alg/monoid_max_idx.hpp" template struct Monoid_Max_Idx { using value_type = pair; using X = value_type; static X op(X x, X y) { return max(x, y); } static constexpr X unit() { return {-INF, -1}; } static constexpr bool commute = true; }; #line 5 "main.cpp" // (dp val, 1個前, 2個前) を 2 個持つ。 // 同じ「2個前」は 1 つまでしか持たないようにする。 struct Mono { using value_type = tuple; using X = value_type; static X _add(X x, ll dp3, ll a3, ll b3) { auto [dp1, a1, b1, dp2, a2, b2] = x; if (b1 == b3 && dp1 < dp3) { return {dp3, a3, b3, dp2, a2, b2}; } if (b2 == b3 && dp2 < dp3) { return {dp1, a1, b1, dp3, a3, b3}; } if (b1 == b3 || b2 == b3) return x; if (dp1 < dp2) { swap(dp1, dp2), swap(a1, a2), swap(b1, b2); } if (dp2 < dp3) return {dp1, a1, b1, dp3, a3, b3}; return x; } static X add(X x, ll dp3, ll a3, ll b3) { x = _add(x, dp3, a3, b3); auto& [dp1, a1, b1, dp2, a2, b2] = x; if (dp1 < dp2) { swap(dp1, dp2), swap(a1, a2), swap(b1, b2); } return x; } static X op(X x, X y) { if (get<0>(x) == -1) return y; if (get<0>(y) == -1) return x; auto [a, b, c, d, e, f] = y; x = add(x, a, b, c); x = add(x, d, e, f); return x; } static constexpr X unit() { return {-1, -1, -1, -1, -1, -1}; } static constexpr bool commute = true; }; void solve() { LL(N); VEC(ll, A, N); auto key = A; UNIQUE(key); for (auto&& a: A) a = LB(key, a) + 5; using X = Mono::X; N = len(key) + 10; SegTree seg_hi(N), seg_lo(N); for (auto&& a: A) { { X x = seg_lo[a]; x = Mono::add(x, 1, a, a + 1); x = Mono::add(x, 1, a, a + 2); auto upd = [&](ll l, ll r) -> void { if (l >= r) return; auto [dp3, a3, b3, dp4, a4, b4] = seg_hi.prod(l, r); if (b3 != a) x = Mono::add(x, dp3 + 1, a, a3); if (b4 != a) x = Mono::add(x, dp4 + 1, a, a4); }; auto [dp1, a1, b1, dp2, a2, b2] = seg_hi.prod(a + 1, N); upd(a + 1, N); if (a1 > a2) swap(a1, a2); chmax(a1, a + 1); chmax(a2, a + 1); upd(a + 1, a1); upd(a1, a1 + 1); upd(a1 + 1, a2); upd(a2, a2 + 1); upd(a2 + 1, N); seg_lo.set(a, x); } { X x = seg_hi[a]; x = Mono::add(x, 1, a, a - 1); x = Mono::add(x, 1, a, a - 2); auto upd = [&](ll l, ll r) -> void { if (l >= r) return; auto [dp3, a3, b3, dp4, a4, b4] = seg_lo.prod(l, r); if (b3 != a) x = Mono::add(x, dp3 + 1, a, a3); if (b4 != a) x = Mono::add(x, dp4 + 1, a, a4); }; auto [dp1, a1, b1, dp2, a2, b2] = seg_lo.prod(0, a); upd(0, a); if (a1 > a2) swap(a1, a2); chmin(a1, a - 1); chmin(a2, a - 1); upd(0, a1); upd(a1 + 1, a2); upd(a2 + 1, a); seg_hi.set(a, x); } // print(a, "lo", seg_lo[a]); // print(a, "hi", seg_hi[a]); } ll ANS = 0; { auto [dp1, a1, b1, dp2, a2, b2] = seg_lo.prod_all(); chmax(ANS, dp1); chmax(ANS, dp2); } { auto [dp1, a1, b1, dp2, a2, b2] = seg_hi.prod_all(); chmax(ANS, dp1); chmax(ANS, dp2); } if (ANS <= 2) ANS = 0; print(ANS); } signed main() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << setprecision(15); ll T = 1; // LL(T); FOR(_, T) solve(); return 0; }