#include <bits/stdc++.h>
using i64 = long long;
#ifdef DEBUG
#include "debug.h"
#else
#define debug(...) void(23)
#endif
constexpr int inf = int(1E9);
template<typename T>
bool chmax(T& a, T b) {
if (a < b) {
a = b;
return true;
}
return false;
}
int main() {
std::ios_base::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> minl(N, inf), minr(N, inf);
for (int i = 0; i < N; ++i) {
if (A[i] == -1) {
minl[i] = 0;
minr[i] = 0;
}
}
for (int i = 1; i < N; ++i) {
minl[i] = std::min(minl[i], minl[i - 1] + 1);
}
for (int i = N - 2; i >= 0; --i) {
minr[i] = std::min(minr[i], minr[i + 1] + 1);
}
std::vector<std::vector<int>> f(N, std::vector<int>(3 * N + 1, -inf));
f[0][0] = 0;
for (int i = 0; i < N; ++i) {
if (A[i] <= 0) {
continue;
}
std::vector<std::vector<int>> g = f;
for (int j = 0; j < N; ++j) {
int d = std::abs(i - j);
for (int k = 0; k <= 3 * N; ++k) {
if (f[j][k] < 0) {
continue;
}
debug(j, k, f[j][k]);
for (int a = 1; a <= A[i]; ++a) {
if (minl[i] != inf) {
int go = i - minl[i];
int need = d + (2 * a - 2) * std::min(minl[i], minr[i]);
if (k + need <= 2 * i) {
int tim = need + minl[i];
debug(go, k + tim, f[j][k] + a);
chmax(g[go][k + tim], f[j][k] + a);
}
}
if (minr[i] != inf) {
int go = i + minr[i];
int need = d + (2 * a - 2) * std::min(minl[i], minr[i]);
if (k + need <= 2 * i) {
int tim = need + minr[i];
debug(go, k + tim, f[j][k] + a);
chmax(g[go][k + tim], f[j][k] + a);
}
}
}
}
}
f = std::move(g);
debug();
}
int ans = 0;
for (int i = 0; i < N; ++i) {
for (int j = 0; j <= 3 * N; ++j) {
chmax(ans, f[i][j]);
}
}
i64 sum = 0;
for (int i = 0; i < N; ++i) {
if (A[i] >= 0) {
sum += A[i];
}
}
std::cout << sum - ans << '\n';
return 0;
}
