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

#define quick ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define mem(a,b) memset(a,b,sizeof a)
#define pb push_back
#define fi first
#define se second

const int INF=0x3f3f3f3f;
const ll L_INF=9223372036854775807;
const double eps = 1e-9;
const int mod = 1e9+7;
const int N=5e5+5;


int n,m;
int s=0;

void run(){
    cin>>n;
    s=1500;
    int f=1;
    for(int i=1;i<=n;i++){
        cin>>m;
        s+=m;
        if(s>=4000){
            cout<<i<<'\n';
            f=0;
            break;
        }
    }
    if(f==1){
        cout<<-1<<'\n';
    }
    
}

int main(){
    quick;
    int T=1;
    //cin>>T;
    while(T--){
         run();
    }
    return 0;
}

/*

*/