#include <iostream>
#include <iomanip>
using namespace std;
bool prim(int a) {
if (a % 2 == 0)
return false ;
for (int d = 3 ; d * d <= a ; d += 2) {
if (a % d == 0)
return false ;
}
return true ;
}
int main() {
int n, i, j, a, sum = 0, cate = 0 ;
cin >> n ;
for (i = 1 ; i <= n ; ++ i) {
cin >> a ;
if (prim(a) == true)
sum += a, cate ++ ;
}
int rez = (sum * 100) / cate ; /// in loc sa calculez 23 / 3 am facut
///2300 / 3 care da 766, pe care l-am impartit la 100
cout << rez / 100 << "." << rez % 100 ;
return 0 ;
}
