#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n, c = 0, s = 0;
  cin >> n;
  int arr[n];
  for (int i = 0; i < n; ++i) {
    cin >> arr[i];
    if (arr[i] == -1 && s) {
      s--;
    } else if (arr[i] == -1) {
      c++;
    } else {
      s += arr[i];
    }
  }
  cout << c;
}
