import java.util.Scanner;

public class Yukicoder75 {

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

		int num;
		double count = 0, sum = 0;
		for (int i = 0; i < 800000; i++) {
			num = 0;
			while (num < K) {
				num += (int) (Math.random() * 6 + 1);
				count++;
			}
			if (num == K) {
				sum++;
			}
		}
		System.out.println(count / sum);
	}
}