#include <iostream>
using namespace std;
int main() {
int sum = 0, total = 0, number;
cin >> number;
while (number > 0) {
if (9 < number && number < 100) {
sum += number;
++total;
}
cin >> number;
}
if (total > 0) {
cout << (1.0 * sum) / total << "\n";
} else {
cout << "NO" << "\n";
}
return 0;
}
