学步园

import java.util.Scanner;
public class Main{	
	public static void main(String[] args) {
		Scanner input=new Scanner(System.in);
		while(true){
			int n=input.nextInt();
			if(n==0)
				break;
			double sum=0;
			for(int i=2;i<=n;i++){
				sum+=(n-i+1)*(1.0/i);
			}
			sum=sum*2+n;
			System.out.printf("%.2f",sum);
			System.out.println();
		}
	}
}