#include<stdio.h>

#include<math.h>

double score[100];

double n,ans;

int main(){

while(scanf("%lf",&n)!=EOF){

for(int i=0;i<n;i++){

scanf("%lf",&score[i]);

ans+=score[i];

}

if((ans/n)>59){

printf("no\n");

}else{

printf("yes\n");

}

ans=0;

}

}