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

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var dp = Enumerable.Repeat(-1.0, n + 1).ToArray();
        WriteLine(DFS(n, dp));
    }
    static double DFS(int a, double[] dp)
    {
        if (dp[a] >= 0) return dp[a];
        if (a == 1)
        {
            dp[a] = 0;
            return dp[a];
        }
        var p = PList(a);
        var count = new int[p.Count];
        for (var i = p.Count - 1; i >= 0; --i)
        {
            var c = a / p[i];
            for (var j = i + 1; j < p.Count; ++j) if (p[j] % p[i] == 0) c -= count[j];
            count[i] = c;
        }
        var sum = 0.0;
        for (var i = 0; i < p.Count - 1; ++i)
        {
            sum += DFS(p[i], dp) * count[i];
        }
        dp[a] = (sum / a + 1) * a / (a - 1);
        return dp[a];
    }
    static List<int> PList(int n)
    {
        var ans = new List<int>();
        var rev = new List<int>();
        for (var i = 1; i * i <= n; ++i)
        {
            if (n % i == 0)
            {
                ans.Add(i);
                if (i * i < n) rev.Add(n / i);
            }
        }
        rev.Reverse();
        return ans.Concat(rev).ToList();
    }
}