using System;

class Program
{
    public static void Main(string[] args)
    {
        var k = int.Parse(Console.ReadLine());
        double[] expectations = new double[30];
        expectations[k] = 0;
        for(int i = k-1;i >= 0;i--)
        {
            double sum = 1;
            for (int j = 1; j <= 6; j++)
            {
                sum += 1 / 6d * expectations[j + i];
            }
            expectations[i] = sum;            
        }
        Console.WriteLine(expectations[0]);

    }
}