#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<cctype>
#include<cstdlib>
#include<algorithm>
#include<bitset>
#include<cstdio>
#include<cstring>
#include<string>
#include<cctype>
#include<cstdlib>
#include<algorithm>
#include<bitset>
#include<vector>
#include<list>
#include<deque>
#include<queue>
#include<map>
#include<set>
#include<stack>
#include<cmath>
#include<sstream>
#include<fstream>
#include<iomanip>
#include<ctime>
#include<complex>
#include<functional>
#include<climits>
#include<cassert>
#include<iterator>
#include<quadmath.h>
using namespace std;

#define MAX 21
int n;


int main(){
	cin >> n;
	__float128 ans = 0;
	for (int i = 0; i < n; i++){
		if (i == 0){
			ans += 1.0;
			continue;
		}
		if (i == 1){
			ans += 1.0;
			continue;
		}
		for (int j = 0; j + 1 < i; j++){
			for (int k = 1; k <= i; k++){
				for (int kk = 1; kk <= i; kk++){
					if (k != kk){
						__float128 F = k*kk;
						F /= (__float128)(i);
						F /= (__float128)(i - 1);
						F /= (__float128)(i + 1);
						ans += F;
					}
				}
			}
		}
		ans += (__float128)((__float128)1.0 / ((__float128)i + (__float128)1.0))*(__float128)(2.0);
	}
	double outt = ans;
	printf("%.16f\n", outt);
	return 0;
}