using System;

public class Hello
{
    public static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = Array.ConvertAll(line, int.Parse);
        Array.Sort(a);
        var sum = 0;
        for (int i = 1; i <= 4; i++) sum += a[i];
        Console.WriteLine("{0:0.00}", sum / 4d);
    }
}