package no352;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		System.out.printf("%.7f\n",solve(n));
	}

	public static double solve(int n) {
		double[] fact = new double[n+1];
		fact[0] = 1;
		for(int i=1;i<=n;i++) {
			fact[i] = fact[i-1] * i;
		}
		double sum = 0;
		for(int i=1;i<=n;i++) {
			for(int j=i+1;j<=n;j++) {
				int m = n - Math.max(i,j);
				double pattern = 0;
				for(int k=1;k<=m;k++) {
					pattern += fact[m] / fact[m-k] * fact[n-k-1] * 2;
				}
				sum += pattern * (i * j - 1) / fact[n];
			}
		}
		sum += n;
		return sum;
	}

}