#include<bits/stdc++.h>
#define int long long
#define pb push_back
namespace IO {
    #define int long long 
    #define gh getchar
    inline int read(){char ch=gh();int x=0;bool t=0;while(ch<'0'||ch>'9')   t|=ch=='-',ch=gh();while(ch>='0'&&ch<='9') x=x*10+(ch^48),ch=gh();return t?-x:x;}
    inline char getc(){char ch=gh();while(ch<'a'||ch>'z') ch=gh();return ch;}
    inline void write(int x){if(x < 0){putchar('-');x = -x;}if(x > 9){write(x / 10);}putchar((x % 10 + '0'));}
}
using namespace IO;
using namespace std;
const int Maxn = 100010, mod = 1e8;
int a[Maxn];
signed main(){
    int n = read(), sm = 1500;
    for(int i = 1; i <= n; i++){
        a[i] = read();
        sm += a[i];
        if(sm >= 4000){
            cout << i << endl;
            return 0;
        }
    }
    puts("-1");
}