input: 
  def findGCD(a, b): 
      """ Find the greatest common divisor (GCD) of two numbers.
      >>> findGCD(1000, 500)
      500
      >>> findGCD(84, 18)
      6
      """
      if (b == 0): 
          return a
      return findGCD(b, a % b)
      
  a = 1000
  b = 500
  print("GCD of number is: ", findGCD(a, b))
  
output:     while b != 0:
          a, b = b, a % b
      return a