import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int K = scan.nextInt();
		scan.close();
		int n = 10000;
		int a;
		if(K % 6 != 0) {
			a = K / 6 + 1;
		}else {
			a = K / 6;
		}
		int cnt = 0;
		double ans = 0;
		for(int i = 0; i < n; i++) {
			int p = 0;
			for(int j = 1; j <= K; j++) {
				p += (int)(Math.random() * 6) + 1;
				if(p >= K) {
					cnt += j;
					break;
				}
			}
		}
		ans += (double) cnt / n;
		System.out.println(ans);

	}
}