import extensions;

fib(n)
{
   if (n < 0)
      { InvalidArgumentException.raise() };

   ^ (n) {
      if (n > 1)
      {
         ^ this self(n - 2) + (this self(n - 1))
      }
      else
      {
         ^ n
      }
   }(n)
}

public program()
{
   for (int i := -1; i <= 10; i += 1)
   {
      Console.print("fib(",i,")=");
      try
      {
         Console.printLine(fib(i))
      }
      catch(Exception e)
      {
         Console.printLine("invalid")
      }
   };

   Console.readChar()
}