#include <bits/stdc++.h>

using namespace std;
#define endl "\n"
typedef long long ll;
void solved() {
  int n;
  cin >> n;
  int a[n + 1];
  for (int i = 1; i <= n; i++) cin >> a[i];
  int ans = 1500;
  for (int i = 1; i <= n; i++) {
    ans += a[i];
    if (ans >= 4000) {
      cout << i << endl;
      return;
    }
  }
  cout << -1 << endl;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  /*int t = 1;
  cin >> t;
  while (t--)*/
  solved();

  return 0;
}