#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>

using namespace std;

int gcd (int x, int y) {
    while (0 < x) {
        int t = x;
        x = y % x;
        y = t;
    }
    return y;
}

int main () {
    int N; cin >> N;

    vector<double> memo(N + 1, -1);
    auto E = [&] (auto self, int x) -> double {
        if (memo[x] != -1) return memo[x];
        if (x == 1) return 0;
        double res = 1;

        for (int v = 1; v < x; v++) {
            res += 1 + self(self, gcd(v, x));
        }

        return memo[x] = res / (x - 1);
    };

    cout << setprecision(10);
    cout << E(E, N) << "\n";
}