Java :

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
	     Scanner input = new Scanner(System.in);
        int number = input.nextInt();
        
	
			    double sum=0,a=1,b; //改成double
			  
			    for(a=1;a<number;a++)
			    {
			      b=a+2;
			     sum=sum+a/b;
			     a++;
			    }
			    System.out.print(sum);
			    
			 }
			}