#include<bits/stdc++.h>
using namespace std;
using ll = long long;
void solve(){
	int n;
	cin >> n;
	vector<int>a(n + 1);
	int ben = 1500;
	for(int i = 1; i <= n; i++){
		cin >> a[i];
	}
	for(int i = 1; i <= n; i++){
		ben += a[i];
		if(ben >= 4000){
			cout << i << endl;
			return;
		}
	}
	cout << -1 << endl;
} 

int main(){
	int _ = 1;
//	cin >> _;
	while(_--){
		solve();
	}
	return 0;
}