import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		float[] money = new float[12];
		for (int i = 0; i < money.length; i++) {
			money[i] = in.nextFloat();
		}
		float sum =0f;
		for (float d : money) {
			sum+=d;
		}
		System.out.printf("$%.2f", sum/money.length);
	}
}