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

#define gc() getchar()
template <class I> void read(I &s) {
    char c = gc(); for (; !isdigit(c); c = gc());
    for (s = 0; isdigit(c); c = gc()) s = s * 10 + c - 48;
}
int n;
signed main() {
    read(n);
    int x = 1500;
    for (int i = 1; i <= n; ++i) {
        int y;
        scanf("%lld", &y);
        // read(y);
        x += y;
        if (x >= 4000) { printf("%lld\n", i); return 0; }
    }
    puts("-1");
    return 0;
}