import java.beans.IntrospectionException;
import java.util.*;

class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int ans=0;
		for(int i=0;i<200000;i++){
			int count=0;
			int now=0;
			while(true){
				now+=(int)(Math.random()*6)+1;
				count++;
				if(now==n) break;
				if(now>n) now=0;
			}
			ans+=count;
		}
		System.out.println(ans*1.0/200000);
	}
}