#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

using ll = long long;
constexpr int INF = 1001001001;
// constexpr int mod = 1000000007;
constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int K;
    cin >> K;
    vector<double> coeff(K + 1, -1), bias(K + 1, -1);
    auto func = [&](auto&& self, int x) -> pair<double, double> {
        if(coeff[x] != -1)  return {coeff[x], bias[x]};
        if(x == K)  return {coeff[x] = 0, bias[x] = 0};
        double a = 0, b = 0;
        for(int i = 1; i <= 6; ++i){
            if(x + i > K)   a += 1.0 / 6;
            else{
                auto [aa, bb] = self(self, x + i);
                a += aa / 6, b += bb / 6;
            }
        }
        b += 1;
        return {coeff[x] = a, bias[x] = b};
    };
    auto [a, b] = func(func, 0);
    double ans = b / (1 - a);
    cout << fixed << setprecision(10);
    cout << ans << endl;

    return 0;
}