#include<bits/stdc++.h>
#define int long long
using namespace std;
int n;
signed main()
{
	int cur=1500;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		int x;
		scanf("%d",&x);
		cur+=x;
		if(cur>=4000)
		{
			cout<<i<<endl;
			return 0;
		}
	}
	cout<<-1;
	return 0;
}