#include <iostream>
#include <iomanip>
#include <cmath>

using ldouble = long double;
const ldouble PI = std::acos(-1.L);

void solve() {
    int k;
    std::cin >> k;

    if (k == 0) {
        std::cout << PI * PI / 6 << "\n";
        return;
    }

    ldouble ans = 0;
    for (int i = 1; i <= k; ++i) ans += ldouble(1) / i;
    std::cout << ans / k << "\n";
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed << std::setprecision(10);

    solve();

    return 0;
}