#include<iostream>
using namespace std;

int main()
{
long double n, input;
while ( cin >> n ) {
long double sum = 0;
for ( int i = 0; i < n; i++ ) {
cin >> input;
sum += input;
}
sum /= n;
cout << ( ( sum > 59 ) ? "no" : "yes" ) << endl;
}
return 0;
}