#include <bits/stdc++.h>
#define pii pair<int, int>
#define int long long
using namespace std;
const int N = 5e5 + 5;
const int INF = 1e9 + 7;

mt19937 rnd(chrono::duration_cast<chrono::nanoseconds>(chrono::system_clock::now().time_since_epoch()).count());
int randint(int L, int R){
	uniform_int_distribution<int> dist(L, R);
	return dist(rnd);
}

int n;
inline void sol(){
	cin >> n;
	int ans = 1500;
	for(int i=1;i<=n;i++){
		int x;
		cin >> x;
		ans += x;
		if(ans >= 4000){
			return cout << i << endl, void();
		}
	}
	cout << -1;
}

signed main()
{
    ios::sync_with_stdio(0), cin.tie(0);
    int tc = 1;
//    cin >> tc;
    while (tc--)
    {
        sol();
    }
    return 0;
}