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");
        }
        else
        {
            int index = ave.ToString().IndexOf('.');
            if(ave.ToString().Length-1 -index != 2)
            {
                Console.Write("0");
            }
        }
        Console.WriteLine();

    }
}