#define PROBLEM "https://yukicoder.me/problems/no/117"

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

auto Y = [](auto f) {
    return [=](auto&&... args) {
        return f(f, std::forward<decltype(args)>(args)...);
    };
};

using ll = long long;
using std::cout;
using std::cin;
constexpr char endl = '\n';
struct Preprocessing { Preprocessing() { std::cin.tie(0); std::ios::sync_with_stdio(0); }; }_Preprocessing;


signed main() {
    ll n;
    cin >> n;

    constexpr double nil = -1.0;
    std::vector<double> dp(n + 1, nil);
    auto f = Y([&](auto&& self, ll n) -> double {
        if(n == 0) { return 0.0; }
        if(dp[n] != nil) { return dp[n]; }

        double sum = 0.0;
        for(int x = 0; x < n; ++x) {
            int y = n - x - 1;
            sum += self(self, x);
            sum += self(self, y);
        }
        auto ans = sum / n + 1;
        dp[n] = ans;
        return ans;
    });

    cout << std::fixed << std::setprecision(12) << f(n) << endl;
}