#include <iostream>
using namespace std;

double a[12];

int main () {
    int  ans =0;
    for (int i=0; i<12; i++) {
        cin>>a[i];
        ans += a[i]*1000;
    }
    
    ans /= 12;
    
    if (ans %10 >= 5) {
       ans /= 10;
       cout<<"$"<<ans/100<<"."<<ans%100 + 1;
    }
    
    else {
         ans /=10;
         cout<<"$"<<ans/100<<"."<<ans%100;
    }
    
    system ("pause");
    return 0;
}
呵呵！