#include #define M_PI 3.14159265358979323846 // pi using namespace std; typedef long long ll; typedef unsigned long long ull; typedef pair P; typedef tuple t3; typedef tuple t4; #define rep(a,n) for(ll a = 0;a < n;a++) #define repi(a,b,n) for(ll a = b;a < n;a++) #include using namespace std; template void chmax(T& reference, T value) { reference = max(reference, value); } template void chmaxmap(map& m, T key, T value) { if (m.count(key)) { chmax(m[key], value); } else { m[key] = value; } } template void chmin(T& reference, T value) { reference = min(reference, value); } int ceil_pow2(int n) { int x = 0; while ((1U << x) < (unsigned int)(n)) x++; return x; } template struct segtree { public: segtree() : segtree(0) {} segtree(int n) : segtree(std::vector(n, e())) {} segtree(const std::vector& v) : _n(int(v.size())) { log = ceil_pow2(_n); size = 1 << log; d = std::vector(2 * size, e()); for (int i = 0; i < _n; i++) d[size + i] = v[i]; for (int i = size - 1; i >= 1; i--) { update(i); } } void set(int p, S x) { assert(0 <= p && p < _n); p += size; d[p] = x; for (int i = 1; i <= log; i++) update(p >> i); } S get(int p) { assert(0 <= p && p < _n); return d[p + size]; } S prod(int l, int r) { assert(0 <= l && l <= r && r <= _n); S sml = e(), smr = e(); l += size; r += size; while (l < r) { if (l & 1) sml = op(sml, d[l++]); if (r & 1) smr = op(d[--r], smr); l >>= 1; r >>= 1; } return op(sml, smr); } S all_prod() { return d[1]; } template int max_right(int l) { return max_right(l, [](S x) { return f(x); }); } template int max_right(int l, F f) { assert(0 <= l && l <= _n); assert(f(e())); if (l == _n) return _n; l += size; S sm = e(); do { while (l % 2 == 0) l >>= 1; if (!f(op(sm, d[l]))) { while (l < size) { l = (2 * l); if (f(op(sm, d[l]))) { sm = op(sm, d[l]); l++; } } return l - size; } sm = op(sm, d[l]); l++; } while ((l & -l) != l); return _n; } template int min_left(int r) { return min_left(r, [](S x) { return f(x); }); } template int min_left(int r, F f) { assert(0 <= r && r <= _n); assert(f(e())); if (r == 0) return 0; r += size; S sm = e(); do { r--; while (r > 1 && (r % 2)) r >>= 1; if (!f(op(d[r], sm))) { while (r < size) { r = (2 * r + 1); if (f(op(d[r], sm))) { sm = op(d[r], sm); r--; } } return r + 1 - size; } sm = op(d[r], sm); } while ((r & -r) != r); return 0; } private: int _n, size, log; std::vector d; void update(int k) { d[k] = op(d[2 * k], d[2 * k + 1]); } }; struct S { ll v1; ll v2; ll m; bool ok() const { return m <= v1 + v2; } }; S op(S left, S right) { ll v1, v2; if (left.v1 < right.v1) { v1 = left.v1; v2 = min(left.v2, right.v1); } else { v1 = right.v1; v2 = min(left.v1, right.v2); } return { v1, v2, max(left.m, right.m) }; } constexpr ll INF = 1e15; S e() { return S{INF,INF,-INF}; } int main() { ll n; cin >> n; vector as(n); rep(i, n) cin >> as[i]; segtree tree(n+1); rep(i, n) tree.set(i, { as[i], INF, as[i] }); tree.set(n, { -INF, -INF, INF }); ll sum = 0; rep(i, n - 1) { { ll left = i + 1, right = n+1; while (right - left > 1) { ll m = left + right; m /= 2; auto s = tree.prod(i, m); //cout << s.ok() << ":" << i << "," << m << "," << s.v1; //cout << "," << s.v2 << "," << s.m << endl; if (s.ok()) { left = m; } else { right = m; } } sum += left - i - 1; } } cout << sum << endl; return 0; }