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

int main() {
	int n;
	cin >> n;

	if (n == 1) {
		cout << 1 << endl;
		return 0;
	}

	if (n == 2) {
		cout << 2 << endl;
		return 0;
	}

	long double ans = 2;
	for (int i = 2; i < n; i++) {
		long double total = 2.0 / (i + 1);
		for (int p = 1; p <= i - 1; p++) {
			for (int j = 1; j <= i; j++) {
				for (int k = 1; k <= i; k++) {
					if (j == k) continue;
					total += j * k * (1.0 / (i + 1)) * (1.0 / i) * (1.0 / (i - 1));
				}
			}
		}
		ans += total;
	}

	printf("%.20f\n", (double)ans);
}