#include <bits/stdc++.h>
#define rep(i, n) for(long long i = 0; i < (long long)n; i++)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()
using namespace std;

using lint = long long;
using ld = long double;

int main() {
    int k;
    cin >> k;
    vector<ld> v(30, -1);
    auto f = [&](auto f, int x) -> ld {
        if (x >= k) {
            return 0.0;
        }
        if (v[x] != -1) {
            return v[x];
        }
        ld res = 0.0;
        for (int i = 1; i <= 6; i++) {
            res += f(f, x + i);
        }
        res /= 6.0;
        res += 1.0;
        v[x] = res;
        return res;
    };
    cout << fixed << setprecision(20) << f(f, 0) << endl;
}