import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int K = scanner.nextInt();

		double[] dp = new double[K + 1];
		dp[K] = 0;
		for (int i = K - 1; i >= 0; i--) {
			for (int j = 1; j <= 6; j++) {
				if (i + j <= K) {
					dp[i] += dp[i + j] / 6;
				}
			}
			dp[i] += 1;
		}
		System.out.println(dp[0]);
	}

}