#include <iostream>
#include <algorithm>
#include <iomanip>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = uint32_t;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;


template <class T>
ostream& operator<<(ostream& os, vector<T> v) {
    os << "{";
    for (int i = 0; i < v.size(); ++i) {
        if(i) os << ", ";
        os << v[i];
    }
    return os << "}";
}

template <class L, class R>
ostream& operator<<(ostream& os, pair<L, R> p) {
    return os << "{" << p.first << ", " << p.second << "}";
}

template <class T, class U>
vector<T> make_v(U size, const T& init){ return vector<T>(static_cast<size_t>(size), init); }

template<class... Ts, class U>
auto make_v(U size, Ts... rest) { return vector<decltype(make_v(rest...))>(static_cast<size_t>(size), make_v(rest...)); }

template<class T> void chmin(T &a, const T &b){ a = (a < b ? a : b); }
template<class T> void chmax(T &a, const T &b){ a = (a > b ? a : b); }

int main() {
    int k;
    cin >> k;
    auto dp = make_v(k+2, k+6, 0.0);
    dp[0][0] = 1;
    double p = 0, A = 0;
    for (int i = 0; i < k; ++i) {
        for (int j = 0; j < k; ++j) {
            for (int l = 1; l <= 6; ++l) {
                dp[i+1][j+l] += dp[i][j]/6;
            }
        }
        p += dp[i+1][k];
        A += (i+1)*dp[i+1][k];
        for (int j = k+1; j <= k+6; ++j) {
            A += (i+1)*dp[i+1][j];
        }
    }
    cout << A/p << "\n";
    return 0;
}