#include <iostream>
#include <cstdio>
using std :: cin;
using std :: cout;
using std :: endl;
int main()
{
double ans;
double tmp;
ans = 0;
for( int i = 0; i < 12; i++ )
{
cin >> tmp;
ans += tmp;
}
cout << "$" << ans / 12.0<< endl;
return 0;
}




