#include <bits/stdc++.h>
using namespace std;

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

    double dp[30] = {};
    for (int i = K - 1; i >= 0; i--) {
        for (int j = 1; j <= 6; j++) {
            dp[i] += (i + j >= K ? 0.0 : dp[i + j]) / 6.0;
        }
        dp[i] += 1;
    }
    cout << dp[0] << endl;
}