import java.util.Scanner;
public class Main {
public static void main(String[] args) {
int a;
int b;
int c;
double average;
Scanner in=new Scanner(System.in);
a=in.nextInt();
b=in.nextInt();
c=in.nextInt();
average=(a+b+c)/3.0;
System.out.println(String.format("%.2f", average));
}

}