#include <bits/stdc++.h>
using namespace std;

using i64 = long long;
const i64 N = 4000;

int main(void)
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n;
    cin >> n;

    vector<i64> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }

    i64 cur = 1500;
    for (int i = 0; i < n; i++) {
        cur += a[i];
        if (cur >= N) {
            cout << i + 1 << endl;
            return 0;
        }
    }

    cout << -1 << endl;

    return 0;
}