#include<iostream>
#include<cstdio>
using namespace std;
int main(int argc, char** argv)
{
double sum = 0, balance, ave;
for(int i = 0; i < 12; i++)
{
cin >> balance;
sum += balance;
}
ave = (long) (100 * sum / 12 + 0.5) * 1.0 / 100;
printf("$%.2lf", ave);
return 0;
}