import java.util.Scanner;

public class Hello{

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        double[] a;

        double s = 0;

        a = new double[13];

        Scanner in = new Scanner(System.in);

        for(int i = 0; i < 12; i++){

            a[i] = in.nextDouble();

            s += a[i];

        }

        s = (double)s/12;

        System.out.printf("$%.2f", s);

        System.out.println();

    }

}