// No.65 回数の期待値の練習
#include <iostream>
#include <vector>
using namespace std;

int main() {
    int K;
    cin >> K;
    vector<double> dp(K + 1);
    for (int i = K - 1; i >= 0; --i) {
        dp[i] += 1;
        for (int j = 1; j <= 6; ++j) {
            dp[i] += dp[min(i + j, K)] / 6;
        }
    }
    cout << dp[0] << endl;
}