input: def findGCD(a, b): 
      """Returns the greatest common divisor of two numbers.
      >>> findGCD(1000, 500)
      500
      >>> findGCD(20, 30)
      10
      """
      if (b == 0): 
          return a
      return findGCD(b, a % b)
output:     if (b == 0): 
          return a
      return findGCD(b, a % b)