public class Addup
{
  public static void main(String args[])
  {
    int n;
    int sum;

    if(args.length != 1)
    {
      System.out.println("Usage: java Addup <n>");
      System.exit(1);
    }
    n = Integer.parseInt(args[0]);
    sum = sumup2(n);//<-- return address = alpha
    System.out.println("The sum is " + sum);
  }

  public static int sumup2(int n)
  {
    int retval;

    if (n <=  0)
    {
      return 0;
    }
    else
    {
      retval = sumup2(n-1) + n; //<-- return value beta
      return retval;
    }
  }       
}    

/*
s(n) = sum from 0 through n

s(n) = 0 if n == 0
       s(n-1) + n  if n > 0
*/

/*

Stack

public static int sumup(n)
{
  return n*(n+1)/2;
}