using System;
using System.Collections.Generic;
using System.Linq;


class AB {
    static int[] S;
    static void Main() {
       S=Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
        List<int> a = S.ToList();
        a.Remove(a.Max());
        a.Remove(a.Min());
        string ans = string.Format("{0:0.00}", (float)(a[0] + a[1] + a[2] + a[3]) / 4);
        Console.WriteLine(ans);
    }
 
}