import java.util.*;
 

public class Main {
	static double e(int x,int k){
		if(x>=k) return 0;
		return e(x+1,k)/6.0+e(x+2,k)/6.0+e(x+3,k)/6.0+e(x+4,k)/6.0+e(x+5,k)/6.0+e(x+6,k)/6.0+1;
	}
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int k=sc.nextInt();
		System.out.println(e(0,k));
	}
}