public class Program
{
    public static void Main()
    {
        //int num = int.Parse(Console.ReadLine() ?? string.Empty);
        string[] str = (Console.ReadLine() ?? string.Empty).Trim().Split(' ');
        //string str = Console.ReadLine() ?? string.Empty;

        int[] num = new int[str.Length];

        for(int i = 0; i < num.Length; i++)
        {
            num[i] = int.Parse(str[i]);
        }
        Array.Sort(num);

        double ave = 0;

        for(int i = 1;i < num.Length-1;i++)
        {
            ave += (double)num[i];
        }
        ave /= 4;
        Console.Write(ave);

        if (ave.ToString().IndexOf('.') == -1) 
        {
            Console.Write(".00");
        }
        Console.WriteLine();

    }
}