input: def find_GCD(a: int, b: int) -> int:
      """ Returns the Greatest Common Divisor (GCD) of two numbers.
      >>> find_GCD(1000, 500)
      500
      >>> find_GCD(36, 24)
      12
      """
      if b == 0:
          return a
      return find_GCD(b, a % b)
output:     if b == 0:
          return a
      return find_GCD(b, a % b)