using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp9
{
    class Program
    {
        static void MainA(string[] args)
        {
            Console.WriteLine(int.Parse(Console.ReadLine()) < 3200 ? "red" : Console.ReadLine());
        }

        static void MainB(string[] args)
        {
            Console.ReadLine();
            Console.WriteLine(1.0d / Console.ReadLine().Split(' ').Select(x => int.Parse(x)).Select(x => 1.0d / x).Sum());
        }

        static void Main(string[] args)
        {
            int[] arr = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).OrderBy(x => x).ToArray();
            double sum = arr[0];
            var arr2 = arr.Skip(1);
            foreach (var n in arr2)
            {
                sum = (sum + n) / 2;
            }
            Console.WriteLine(sum);
        }
    }
}
