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

using ldouble = long double;
constexpr ldouble INF = 1e20;

void solve() {
    ldouble n;
    std::cin >> n;

    std::cout << std::fixed << std::setprecision(10)
              << std::riemann_zeta(n) << "\n";
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}