using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var dp = Enumerable.Repeat(-1.0, n + 1).ToArray();
        dp[0] = 0;
        WriteLine(Break(n, dp));
    }
    static double Break(int n, double[] dp)
    {
        if (dp[n] >= 0) return dp[n];
        var sum = 0.0;
        for (var i = 0; i < n; ++i)
        {
            sum += Break(i, dp) + Break(n - i - 1, dp) + 1;
        }
        dp[n] = sum / n;
        return dp[n];
    }
}