using System;

public class Solution
{
    private Dictionary<(int, int), double> dp = new Dictionary<(int, int), double>();
    public double SoupServings(int n)
    {
        if (n > 5000)
            return 1.0;

        n = (n + 24) / 25;

        // use dynamic programming
        return Helper(n, n);
    }

    private double Helper(int a, int b)
    {
        if (a <= 0 && b <= 0)
        {
            return 0.5;
        }
        if (a <= 0)
        {
            return 1.0;
        }
        if (b <= 0)
        {
            return 0.0;
        }
        if (dp.ContainsKey((a, b)))
        {
            return dp[(a, b)];
        }

        double probability = 0.25 * (
            Helper(a - 4, b) +
            Helper(a - 3, b - 1) +
            Helper(a - 2, b - 2) +
            Helper(a - 1, b - 3)
        );

        dp[(a, b)] = probability;
        return probability;
    }
}

class Program
{
    static void Main()
    {
        var Solution = new Solution();
        var ans = Solution.SoupServings(800);
        Console.WriteLine(ans);
    }
}