#include <bits/stdc++.h>
#define int long long
#define endl "\n"
#define iosy ios::sync_with_stdio(0),cin.tie(0),cout.tie(0)
#define rep(i,a,n) for(int i=a;i<=n;i++)
#define rop(i,a,n) for(int i=a;i<n;i++)
using namespace std;
const int inf = 0x3f3f3f3f3f3f3f3fLL;
const int N = 2e5+10;
const int MOD = 1e9+7;
void solve(){
	int n;cin>>n;
	vector<int> a(n+1);
	int ans=1500;
	int idx=-1;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		ans+=a[i];
		if(ans>=4000)idx=i;
	}
	if(idx==-1)cout<<"-1\n";
	else cout<<idx<<"\n";
}

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