import java.text.DecimalFormat;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sca = new Scanner(System.in);
		double sum = 0.0;
		for(int i=0; i<12; i++)
		{
			sum += sca.nextDouble();
		}
//		System.out.println("$" + (sum / 12.0));
		DecimalFormat df = new DecimalFormat("0.00");
		System.out.println("$" + df.format(sum / 12.0));
	}
}