#include <cmath>
#include <iomanip>
#include <iostream>
#include <vector>
using namespace std;

#include <numbers>

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

    constexpr int L = 1010101;
    vector<double> invsum(L + 1);
    for (int i = 0; i < L; ++i) invsum.at(i + 1) = invsum.at(i) + 1.0 / (i + 1);

    auto get_invsum = [&](long long n) -> double {
        if (n <= L) return invsum.at(n);
        return log(n) + std::numbers::egamma;
    };

    double ret = get_invsum(N) * 2 - 1;

    long long d = 2;

    while (d <= N) {
        long long k = N / d;
        if (k <= 0) break;
        long long r = N / k;

        ret += (get_invsum(k) - 1) * (get_invsum(r) - get_invsum(d - 1));

        d = r + 1;
    }

    cout << fixed << setprecision(13) << ret << '\n';
}