import java.util.Scanner;

public class A {
    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        double a = cin.nextDouble();
        double b = cin.nextDouble();
        double c = cin.nextDouble();
        double avg = (a + b + c) / 3;
        System.out.println(String.format("%.3f", avg));
        cin.close();
    }
}