// File A.cpp created on 24.11.2025 at 14:47:41
#include <bits/stdc++.h>
using i64 = long long;
#ifdef DEBUG
#include "/home/ahmetalp/Desktop/Workplace/debug.h"
#else
#define debug(...) void(23)
#endif
int main() {
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
int N;
std::cin >> N;
std::vector<int> A(N);
for (int i = 0; i < N; ++i) {
std::cin >> A[i];
}
std::vector<int> disl(N, N), disr(N, N);
for (int i = 0; i < N; ++i) {
if (A[i] == -1) {
disl[i] = 0;
disr[i] = 0;
}
}
for (int i = 1; i < N; ++i) {
disl[i] = std::min(disl[i], disl[i - 1] + 1);
}
for (int i = N - 1; i >= 1; --i) {
disr[i - 1] = std::min(disr[i - 1], disr[i] + 1);
}
debug(disl, disr);
std::vector<int> p;
std::vector<int> ord;
p.reserve(N);
ord.reserve(N);
for (int i = 0; i < N; ++i) {
if (A[i] >= 0) {
ord.emplace_back(i);
} else {
p.emplace_back(i);
}
}
std::sort(ord.begin(), ord.end(), [&](auto lhs, auto rhs) -> bool {
return std::min(disl[lhs], disr[lhs]) < std::min(disl[rhs], disr[rhs]);
});
int n = int(p.size());
std::vector<int> cnt(N);
auto check = [&]() -> bool {
debug(cnt);
auto c = cnt;
int now = 0;
for (int j = 0; j <= n; ++j) {
int l = (j == 0 ? 0 : p[j - 1] + 1);
int r = (j == n ? N : p[j]);
for (int i = l; i < r; ++i) {
if (c[i] == 0) {
continue;
}
while (c[i] > 1) {
debug(i, now);
if (now > i) {
return false;
}
now += std::min(disl[i], disr[i]) * 2;
c[i]--;
}
debug(i, now);
if (now > i) {
return false;
}
int next = i + 1;
while (next < r && c[next] <= 0) {
next++;
}
now += std::min(disl[i] * 2, (disr[i] - next + i) * 2);
}
}
return true;
};
int ans = 0;
for (auto i : ord) {
while (cnt[i] < A[i]) {
cnt[i] += 1;
if (!check()) {
cnt[i] -= 1;
break;
}
ans += 1;
debug(cnt);
}
}
debug(ans);
i64 total = 0;
for (int i = 0; i < N; ++i) {
total += std::max(0, A[i]);
}
std::cout << total - ans << '\n';
return 0;
}
