#include //#include //using namespace atcoder; #pragma GCC target ("avx2") #pragma GCC optimization ("O3") #pragma GCC optimization ("unroll-loops") const double pi = 3.141592653589793238462643383279; using namespace std; //typedef //------------------------------------------ typedef vector VI; typedef vector VVI; typedef vector VS; typedef pair PII; typedef pair PLL; typedef pair TIII; typedef long long LL; typedef unsigned long long ULL; typedef vector VLL; typedef vector VVLL; //container util //------------------------------------------ #define ALL(a) (a).begin(), (a).endf() #define RALL(a) (a).rbegin(), (a).rend() #define PB push_back #define MP make_pair #define SZ(a) int((a).size()) #define SQ(a) ((a) * (a)) #define EACH(i, c) for (typeof((c).begin()) i = (c).begin(); i != (c).endf(); ++i) #define EXIST(s, e) ((s).find(e) != (s).endf()) #define SORT(c) sort((c).begin(), (c).endf()) //repetition //------------------------------------------ #define FOR(i, s, n) for (int i = s; i < (int)n; ++i) #define REP(i, n) FOR(i, 0, n) #define MOD 1000000007 #define rep(i, a, b) for (int i = a; i < (b); ++i) #define trav(a, x) for (auto &a : x) #define all(x) x.begin(), x.end() typedef long long ll; typedef pair pii; typedef vector vi; #define chmin(x, y) x = min(x, y) #define chmax(x, y) x = max(x, y) const double EPS = 1e-4, PI = acos(-1); //ここから編集 typedef string::const_iterator State; template< int mod > struct ModInt { int x; ModInt() : x(0) {} ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {} ModInt &operator+=(const ModInt &p) { if((x += p.x) >= mod) x -= mod; return *this; } ModInt &operator-=(const ModInt &p) { if((x += mod - p.x) >= mod) x -= mod; return *this; } ModInt &operator*=(const ModInt &p) { x = (int) (1LL * x * p.x % mod); return *this; } ModInt &operator/=(const ModInt &p) { *this *= p.inverse(); return *this; } ModInt operator-() const { return ModInt(-x); } ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; } ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; } ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; } ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; } bool operator==(const ModInt &p) const { return x == p.x; } bool operator!=(const ModInt &p) const { return x != p.x; } ModInt inverse() const { int a = x, b = mod, u = 1, v = 0, t; while(b > 0) { t = a / b; swap(a -= t * b, b); swap(u -= t * v, v); } return ModInt(u); } ModInt pow(int64_t n) const { ModInt ret(1), mul(x); while(n > 0) { if(n & 1) ret *= mul; mul *= mul; n >>= 1; } return ret; } friend ostream &operator<<(ostream &os, const ModInt &p) { return os << p.x; } friend istream &operator>>(istream &is, ModInt &a) { int64_t t; is >> t; a = ModInt< mod >(t); return (is); } static int get_mod() { return mod; } }; using modint = ModInt< 998244353 >; template< typename T > struct Combination { vector< T > _fact, _rfact, _inv; Combination(int sz) : _fact(sz + 1), _rfact(sz + 1), _inv(sz + 1) { _fact[0] = _rfact[sz] = _inv[0] = 1; for(int i = 1; i <= sz; i++) _fact[i] = _fact[i - 1] * i; _rfact[sz] /= _fact[sz]; for(int i = sz - 1; i >= 0; i--) _rfact[i] = _rfact[i + 1] * (i + 1); for(int i = 1; i <= sz; i++) _inv[i] = _rfact[i] * _fact[i - 1]; } inline T fact(int k) const { return _fact[k]; } inline T rfact(int k) const { return _rfact[k]; } inline T inv(int k) const { return _inv[k]; } T P(int n, int r) const { if(r < 0 || n < r) return 0; return fact(n) * rfact(n - r); } T C(int p, int q) const { if(q < 0 || p < q) return 0; return fact(p) * rfact(q) * rfact(p - q); } T H(int n, int r) const { if(n < 0 || r < 0) return (0); return r == 0 ? 1 : C(n + r - 1, r); } }; template struct SegmentTree{ int N; vector node; Monoid Unit; function f; SegmentTree(vector v, const function f, const Monoid &Unit): f(f), Unit(Unit){ int sz_ = v.size(); N = 1; while(N < sz_) N *= 2; node.assign(2*N, Unit); for(int i=0; i=0; i--) node[i] = f(node[2*i+1], node[2*i+2]); } void update(int k, const Monoid &x) { k += N-1; node[k] = x; while(k > 0){ k = (k-1)/2; node[k] = f(node[2*k+1], node[2*k+2]); } } Monoid query(int a, int b, int k=0, int l = 0, int r=-1){ if(r < 0) r = N; if(r <= a || b <= l) return Unit; if(a <= l && r <= b) return node[k]; else{ Monoid vl = query(a, b, 2*k+1, l, (l+r)/2); Monoid vr = query(a, b, 2*k+2, (l+r)/2, r); return f(vl, vr); } } }; int f(auto& vp, int N){ vector tmp(N, 0); SegmentTree l(tmp, [&](int a, int b){return max(a, b);}, 0); SegmentTree r(tmp, [&](int a, int b){return max(a, b);}, 0); int res = 0; REP(i,vp.size()){ int idx = vp[i].second; if(i == 0){ l.update(idx, 1); r.update(idx, 1); }else{ int L = l.query(0, idx); int R = r.query(idx+1, N); res = max(res, min(L, R)); l.update(idx, L+1); r.update(idx, R+1); } } return res; } int main() { cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(15); int N; cin >> N; vector a(N); REP(i,N) cin >> a[i]; vector> vp; REP(i,N) vp.push_back({a[i], i}); sort(all(vp)); int t1 = f(vp, N); reverse(all(vp)); int t2 = f(vp, N); cout << max(t1, t2) << endl; return 0; }