////////    File Factorial.java    ///////

// run with      kaffe Factorial 5

import java.lang.Integer;   // for parseInt

public class Factorial
{
    public static int factorial(int n)
    { int ans = 1;
          while (n > 1)
          {    ans = ans * n;       
               n = n - 1;
          } 
      return(ans);
    }

    public static void main(String args[])
    { int j;
          if (args.length != 1)
          {    System.err.println("Factorial takes one integer argument");
               System.exit(1);     // abnormal termination of main
          }
          j = Integer.parseInt(args[0]);  // string to int conversion
          if ( j < 0 )
          {    System.err.println("Arg to Factorial must not be negative");
               System.exit(1);     // abnormal termination of main
          }
          System.out.print("factorial(" + args[0] + ")= ");
          System.out.println(factorial(j));
    }
}