input: 
  def findGCD(a, b):
      """ Find the greatest common divisor (GCD) of two numbers.
      >>> findGCD(1000, 500)
      1000
      >>> findGCD(48, 18)
      6
      """
      if b == 0:
          return a
      return findGCD(b, a % b)
  
output:     if b == 0:
          return a
      return findGCD(b, a % b)