#include <bits/stdc++.h>
// #include <atcoder/all>
// using namespace atcoder;
//using mint = modint1000000007;
#include <string>
#include <vector>
#include <algorithm>
#define rep(i,n) for (int i = 0;i < (n); ++i)
using namespace std;
using ll = long long;
using P = pair<int,int>;
#define chmax(x,y) x = max(x,y)
using R=double;
using ld = long double;
int INF = 2*1e9;
ll LINF = 1e18*9;
int mod = 1000000007;
int mod2 = 1;
using graph = vector<vector<int>>;

const double eps = 1e-10;
template<class T> struct Matrix {
    vector<vector<T> > val;
    Matrix(int n, int m, T x = 0) : val(n, vector<T>(m, x)) {}
    void init(int n, int m, T x = 0) {val.assign(n, vector<T>(m, x));}
    size_t size() const {return val.size();}
    inline vector<T>& operator [] (int i) {return val[i];}
};

template<class T> int GaussJordan(Matrix<T> &A,bool is_extended = false){
	int n = A.size(), m = A[0].size();
	int rank  = 0;
	for(int col = 0;col < m;col++){
		if(is_extended && col == m-1) break;
		int pivot = -1;
		T ma = eps;
		for(int row = rank;row < n;row++){
			if(abs(A[row][col]) > ma){
				ma = abs(A[row][col]);
				pivot = row;
			}
		}

		if(pivot == -1) continue;
		swap(A[pivot],A[rank]);
		auto fac = A[rank][col];
		for(int col2 = 0;col2 < m;col2++) A[rank][col2] /= fac;

		for(int row = 0;row < n;row++){
			if(row != rank && abs(A[row][col]) > eps){
				auto fac = A[row][col];
				for(int col2 = 0;col2 < m;col2++){
					A[row][col2] -= A[rank][col2]*fac;
				}
			}
		}
		rank++;
	}
	return  rank;
}

template<class T> vector<T> LE(Matrix<T> &A,vector<T> &b){
	int n = A.size(),m = A[0].size();
	Matrix<T> M(n,m+1);
	for(int i = 0;i < n;i++){
		for(int j = 0;j < m;j++) M[i][j] = A[i][j];
		M[i][m] = b[i];
	}
	int rank = GaussJordan(M,true);

	vector<T> res;
	for(int row = rank;row < n;row++) if(abs(M[row][m]) > eps) return res;

	res.assign(m,0);
	for(int i = 0;i < rank;i++) res[i] = M[i][m];
	return res;
}

int main(){
	int k;cin >> k;
	vector<double> b(k,1);

	Matrix<double> M(k,k);
	for(int i = k-1;i >= 0;i--){
		M[i][i] = 1;
		for(int j = 1;j <= 6;j++){
			if(i+j==k) continue;
			if(i+j < k) M[i][i+j] = -double(1)/6;
			else M[i][0] += -double(1)/6;
		}
	}

	// for(int i = 0;i < k;i++){
	// 	for(int j = 0;j < k;j ++)cout << M[i][j] << " ";
	// 	cout << b[i] << endl;
	// }
	auto ans = LE(M,b);
	cout << ans[0] << endl;
	//for(int i = 0;i < k;i++) cout << ans[i] << endl;

	
}