using System;

public class Program

{

    public static void Main()

    {

        double input = Convert.ToDouble(Console.ReadLine());

        double result = 0;

        int counter = 0;

        while(input != 0){

            result += input;

            counter++;

            input = Convert.ToDouble(Console.ReadLine());

        }

        Console.WriteLine(result / counter);

    }

}