#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, sum = 0, count = 0;
  cin >> n;
  int a[n];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  for (int i = 0; i < n; i++) {
    if (a[i] != -1) sum = sum + a[i];
    if (a[i] == -1) {
      if (sum != 0)
        sum--;
      else
        count++;
    }
  }
  cout << count << endl;
}
