#include <iostream>

#include <string>

#include <sstream>

#include <cmath>

using namespace std;

int main()

{

int x;

while (cin >> x)

{

int y[20];

float total = 0;

for (int i = 0; i < x; i++)

{

cin >> y[i];

}

for (int i = 0; i < x; i++)

{

total = total + y[i];

}

if (total / x > 59)

{

cout << "no" << endl;

}

else

{

cout << "yes" << endl;

}

}

}