#include <iostream>
#include <cstring>
using namespace std;

const int MAX_K = 300;

double table[MAX_K];

int main() {
    int k;
    cin >> k;

    double lb = 0.0, ub = 1e20;
    for (int i = 0; i < 10000; i++) {
        double mid = (lb + ub) / 2.0;
        memset(table, 0.0, sizeof(table));
        table[k] = 0.0;

        for (int v = k - 1; v >= 0; v--) {
            for (int d = 1; d <= 6; d++) {
                double value;
                if (v + d > k) value = mid;
                else value = table[v + d];
                table[v] += (value + 1) * (1.0 / 6.0);
            }
        }

        if (table[0] >= mid) {
            lb = mid;
        } else {
            ub = mid;
        }
    }
    cout << lb << endl;

    return 0;
}