import java.util.Scanner;

public class Main {
	public static void main(String[] agse) {
		Scanner sc =new Scanner(System.in);
		int a =sc.nextInt();
		int b =sc.nextInt();
		int c =sc.nextInt();
		double g =(a+b+c)/3.0;
		System.out.println(String.format("%.3f",g));
	}
}
/**************************************************************
	Problem: 1957
	User: admin
	Language: Java
	Result: Accepted
	Time:767 ms
	Memory:40068 kb
****************************************************************/