// >>> TEMPLATES #include using namespace std; using ll = long long; using ld = long double; using i32 = int32_t; using i64 = int64_t; #define int ll #define double ld #define rep(i,n) for (int i = 0; i < (int)(n); i++) #define rep1(i,n) for (int i = 1; i <= (int)(n); i++) #define repR(i,n) for (int i = (int)(n)-1; i >= 0; i--) #define rep1R(i,n) for (int i = (int)(n); i >= 1; i--) #define loop(i,a,B) for (int i = a; i B; i++) #define loopR(i,a,B) for (int i = a; i B; i--) #define all(x) (x).begin(), (x).end() #define allR(x) (x).rbegin(), (x).rend() #define pb push_back #define eb emplace_back #define mp make_pair #define fst first #define snd second auto constexpr INF32 = numeric_limits::max()/2-1; auto constexpr INF64 = numeric_limits::max()/2-1; auto constexpr INF = numeric_limits::max()/2-1; #ifdef LOCAL #include "debug.hpp" #define dump(...) cerr << "[" << setw(3) << __LINE__ << ":" << __FUNCTION__ << "] ", dump_impl(#__VA_ARGS__, __VA_ARGS__) #define say(x) cerr << "[" << __LINE__ << ":" << __FUNCTION__ << "] " << x << endl #define debug if (1) #else #define dump(...) (void)(0) #define say(x) (void)(0) #define debug if (0) #endif template using pque_max = priority_queue; template using pque_min = priority_queue, greater >; template ::value>::type> ostream& operator<<(ostream& os, T const& v) { bool f = true; for (auto const& x : v) os << (f ? "" : " ") << x, f = false; return os; } template ::value>::type> istream& operator>>(istream& is, T &v) { for (auto& x : v) is >> x; return is; } template istream& operator>>(istream& is, pair& p) { return is >> p.first >> p.second; } struct IOSetup { IOSetup() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); } } iosetup; template struct FixPoint : private F { constexpr FixPoint(F&& f) : F(forward(f)) {} template constexpr auto operator()(T&&... x) const { return F::operator()(*this, forward(x)...); } }; struct MakeFixPoint { template constexpr auto operator|(F&& f) const { return FixPoint(forward(f)); } }; #define MFP MakeFixPoint()| #define def(name, ...) auto name = MFP [&](auto &&name, __VA_ARGS__) template struct vec_impl { using type = vector::type>; template static type make_v(size_t n, U&&... x) { return type(n, vec_impl::make_v(forward(x)...)); } }; template struct vec_impl { using type = T; static type make_v(T const& x = {}) { return x; } }; template using vec = typename vec_impl::type; template auto make_v(Args&&... args) { return vec_impl::make_v(forward(args)...); } template void quit(T const& x) { cout << x << endl; exit(0); } template constexpr bool chmin(T& x, U const& y) { if (x > y) { x = y; return true; } return false; } template constexpr bool chmax(T& x, U const& y) { if (x < y) { x = y; return true; } return false; } template constexpr auto sumof(It b, It e) { return accumulate(b,e,typename iterator_traits::value_type{}); } template int sz(T const& x) { return x.size(); } template int lbd(C const& v, T const& x) { return lower_bound(v.begin(), v.end(), x)-v.begin(); } template int ubd(C const& v, T const& x) { return upper_bound(v.begin(), v.end(), x)-v.begin(); } template int ppt(C const& v, F f) { return partition_point(v.begin(), v.end(), f)-v.begin(); } // <<< // >>> BIT struct BIT { int n; vector v; // use v[1..n] BIT(int n) : n(n), v(n+1) {} int size() const { return n; } int get(int i) const { return sum(i+1)-sum(i); } void set(int i, int x) { add(i,x-get(i)); } void add(int i, int x) { assert(0 <= i); assert(i < n); for (i++; i <= n; i += i&(-i)) v[i] += x; } int sum(int r) const { // [0,r) assert(0 <= r); assert(r <= n); int s = 0; for (int i = r; i > 0; i -= i&(-i)) s += v[i]; return s; } int sum(int l, int r) const { // [l,r) return sum(r)-sum(l); } }; // <<< int32_t main() { int n; cin >> n; vector p(n); cin >> p; vector pos(n); rep (i,n) pos[--p[i]] = i; vector> min_rng(n),max_rng(n),tmp(n); rep (i,n) min_rng[i] = max_rng[i] = mp(i,i+1); rep (i,n) { int x = pos[i]; if (x+1 < n && p[x+1] < i) chmax(max_rng[x].snd, tmp[x+1].snd); if (x-1 >= 0 && p[x-1] < i) chmin(max_rng[x].fst, tmp[x-1].fst); tmp[max_rng[x].snd-1].fst = max_rng[x].fst; tmp[max_rng[x].fst].snd = max_rng[x].snd; } repR (i,n) { int x = pos[i]; if (x+1 < n && p[x+1] > i) chmax(min_rng[x].snd, tmp[x+1].snd); if (x-1 >= 0 && p[x-1] > i) chmin(min_rng[x].fst, tmp[x-1].fst); tmp[min_rng[x].snd-1].fst = min_rng[x].fst; tmp[min_rng[x].fst].snd = min_rng[x].snd; } dump(min_rng); dump(max_rng); vector> wmin(n+1),wmax(n+1); rep (i,n) { wmin[min_rng[i].snd].eb(i); wmax[max_rng[i].snd].eb(i); } BIT bit_min(n), bit_max(n); int cnt = 0; rep (i,n) { dump(i); dump(bit_min.sum(max_rng[i].fst,i)); cnt += bit_min.sum(max_rng[i].fst,i); bit_min.add(i,+1); for (int idx : wmin[i+1]) { bit_min.add(idx,-1); } dump(bit_max.sum(min_rng[i].fst,i)); cnt += bit_max.sum(min_rng[i].fst,i); bit_max.add(i,+1); for (int idx : wmax[i+1]) { bit_max.add(idx,-1); } } cout << cnt << endl; }