import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {
	
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		final int k = sc.nextInt();
		
		double[] DP = new double[k + 6];
		for(int cur = k - 1; cur >= 0; cur--){
			DP[cur] = 1;
			for(int i = 1; i <= 6; i++){
				DP[cur] += DP[cur + i] / 6;
			}
		}
		
		System.out.printf("%.8f\n", DP[0]);
		
	}
	
}