import java.util.*;

public class Main {
	
	
  public static void main(String[] args) {
	  Scanner sc=new Scanner(System.in);
	  int k=sc.nextInt();
	  Random r=new Random();
	  int ans=0;
	  int i=0;
	  while(i<1000000){
		  int sum=0;
		  int t=0;
		  while(true){
		  int n=r.nextInt(6)+1;
		  t++;
		  sum+=n;
		  if(sum>k)sum=0;
		  else if(sum==k)break;
		  }
		  ans+=t;
		  i++;
	  }
	  System.out.println((double)ans/2000000);
	  	  
  }
}