#include <bits/stdc++.h>
// #pragma GCC optimize(2)
#ifndef ONLINE_JUDGE
    #define Debug
#endif
#define multiple_test 0
#define int int64_t
const int MAXN = 1e6, N = MAXN + 10;
const int MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f3f3f3f3fll;
using namespace std;

inline void solve() {
    int n; cin >> n;
    vector<int> a(n + 1);
    for(int i = 1; i <= n; i++) {
        cin >> a[i];
    }
    int res = 1500;
    for(int i = 1; i <= n; i++) {
        res += a[i];
        if(res >= 4000) {
            cout << i << "\n";
            return;
        }
    }
    cout << "-1\n";
}

signed main() {
#ifndef ONLINE_JUDGE
    // freopen("in.txt", "r", stdin);
    // freopen("out.txt", "w", stdout);
    clock_t start_time = clock();
#else
    ios::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
#endif 
    int t = 1; if(multiple_test) cin >> t;
    while(t--) {
        solve();
    }
#ifndef ONLINE_JUDGE
    cout << "Used " << clock() - start_time << " ms" << endl;
#endif
    return 0;
}