import java.util.Scanner;
import java.lang.Math;
public class Main{
public static void main(String[] args){
Scanner scan = new Scanner(System.in);
int a = scan.nextInt();
int b = scan.nextInt();
int c = scan.nextInt();
double d = (a + b + c) / 3.0;
System.out.println(String.format("%.6f",d));
}
}