#include <bits/stdc++.h>
using namespace std;

using ld = long double;

int main() {
    int n;
    cin >> n;
    vector<ld> dp(n + 1, -1);
    auto f = [&](auto f, int x) -> ld {
        if (x <= 1) {
            return x == 1 ? 1.0 : 0.0;
        }
        if (dp[x] != -1) {
            return dp[x];
        }
        ld res = 1.0;
        for (int y = 0; y < x; y++) {
            int a = y, b = x - 1 - y;
            ld p = 1.0 / (ld)x;
            res += (f(f, a) + f(f, b)) * p;
        }
        dp[x] = res;
        return res;
    };
    cout << fixed << setprecision(15) << f(f, n) << endl;
}