#include<stdio.h>

int main(){

int i;

int total;

int n;

int a;

int average;

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

for(i=1;i<=n;i++){

total=0;

scanf("%d",&a);

total=total+a;

}

average=(double)total/n;

if(average>59){

printf("no\n");

}

else{

printf("yes\n");

}

}

return 0;

}