#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>
#include <functional>
#include <set>
#include <ctime>
#include <random>
#include <chrono>
using namespace std;

template<class T> istream& operator >> (istream& is, vector<T>& vec){for(T& val: vec) is >> val; return is;}
template<class T> istream& operator ,  (istream& is, T& val){ return is >> val;}
template<class T> ostream& operator << (ostream& os, const vector<T>& vec){for(int i=0; i<vec.size(); i++) os << vec[i] << (i==vec.size()-1?"":" "); return os;}
template<class T> ostream& operator ,  (ostream& os, const T& val){ return os << " " << val;}
template<class T> ostream& operator >> (ostream& os, const T& val){ return os << " " << val;}

using Real = long double;

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

	if(n==1){
		cout << 1 << endl;
		return 0;
	}
	if(n==2){
		cout << 2 << endl;
		return 0;
	}

	vector<Real> f(n+1, 1.0);
	for(int k=2; k<=n; k++){
		f[k] = k * f[k-1];
	}

	Real ans = 2;
	for(int i=3; i<=n; i++){
		for(int l=1; l<=i-1; l++){
			for(int r=l+1; r<=i-1; r++){
				Real cost = l*r;
				ans += cost * 2.0 * f[i-2] / f[i] ;
			}
		}
		ans += 1 * 2.0 / i;
	}

	printf("%.16f\n", (double)ans);

	return 0;
}