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