// HW08_2a.java
// Tim Hilby
// Created on April 12, 2006
import java.util.Scanner;

public class HW08_2a
{
   // calculates the sum from lo to hi (inclusive)
   public static int sum(int lo, int hi)
   {
      if (lo > hi)
      {
         // the range is not valid
         return 0;
      }
      else if (lo == hi)
      {
         // trivial base case
         // (the sum from x to x is x)
         return lo;
      }
      else
      {
         // sum of the whole is equal to
         // the sum of the left plus the right
         int avg = (lo + hi) / 2;
         return (sum(lo, avg) + sum(avg + 1, hi));
      }
   }

   public static void main(String[] args)
   {
      Scanner scan = new Scanner(System.in);
      
      System.out.print("This program calculates the ");
      System.out.println("sum of numbers from one to N.");
      
      int n;
      System.out.println("What is N? (type 0 to quit)");
      n = scan.nextInt();
      while (n != 0)
      {
         System.out.println("Answer: " + sum(1, n));
         System.out.println("What is N? (type 0 to quit)");
         n = scan.nextInt();
      }
   }
}