input: 
  def findGCD(a, b):
      """Compute the Greatest Common Divisor (GCD) of two numbers using the Euclidean algorithm.
      >>> findGCD(1000, 500)
      500
      >>> findGCD(48, 18)
      6
      """
      if (b == 0): 
          return a
      return findGCD(b, a % b)
  
output:     while b != 0:
          a, b = b, a % b
      return a