#define _USE_MATH_DEFINES
 
#include <iostream>
#include <iomanip>
#include <sstream>
 
#include <algorithm>
#include <cmath>
 
#include <string>
//#include <array>
#include <list>
#include <queue>
#include <vector>
#include <complex>
#include <set>
#include <map>
 
/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
 
#define PII pair<int,int>
/////////
typedef long long LL;
typedef long double LD;
/////////
using namespace::std;
/////////

int main(void){
    std::cin.tie(0); 
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed;//
    cout << setprecision(16);//
	
	int K;
	cin >> K;
	vector<LD> E(K+6);
	vector<LD> C(K+6);
	rep(i,K+6){
		E[i] = 0;
		C[i] = 0;
	}
	rep(i,5){
		E[K+1+i] = 1;
	}
	for(int i = K-1; i>=0; --i){
		for(int j=1;j<=6;++j){
			E[i] += E[i+j];
			C[i] += C[i+j];
		}
		E[i] /= 6.0;
		C[i] /= 6.0;
		C[i] += 1.0;
	}
	LD ans;

	ans = C[0]/(1-E[0]);
	P(ans);
	return 0;
}