/* File: FacRec.java - March 2011 */
package l04;

/**
 * Compute and display the factorial of the input argument
 * using a recursive algorithm
 *
 * Sample usage: java l04.FacRec 5
 *
 * @author Michael Albert
 *
 */

public class FacRec{

   public static void main(String[] args) {
      int n = Integer.parseInt(args[0]);
      System.out.println(n + "! = " + factorial(n));
   }

  public static long factorial(int n) {
      if (n < 0) throw new ArithmeticException("Factorial not defined on " + n);
      if (n == 0) return 1;
      return n*factorial(n-1);
   }

}