#include <bits/stdc++.h>
using namespace std;
int read(){
	int ret=0,f=1;char ch=getchar();
	while(!isdigit(ch)){if(ch=='-')f=-f;ch=getchar();}
	while( isdigit(ch)){ret=(ret<<3)+(ret<<1)+(ch&15);ch=getchar();}
	return ret*f;
}
int n,now;
int main(){
	n=read();now=1500;
	for(int i=1;i<=n;++i){
		int v=read();
		now+=v;
		if(now>=4000){
			printf("%d\n",i);
			return 0;
		}
	}
	printf("-1\n");
	return 0;
}