import java.util.*;

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