import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double[] dp = new double[n + 6];
        for (int i = n - 1; i >= 0; i--) {
            dp[i] = 1;
            for (int j = 1; j <= 6; j++) {
                dp[i] += dp[i + j] / 6;
            }
        }
        System.out.println(dp[0]);
    }
}