using System;

public class Program

{

    public static void Main()

    {

            int n = Convert.ToInt32(Console.ReadLine());

            double average = 0;

​

            while (n != 0)

            {

                average = (average + n) / 2;

                n = Convert.ToInt32(Console.ReadLine());

            }

            Console.WriteLine(average);

    }

}