input: def findGCD(a, b): 
     """ Find the GCD of two numbers.
     >>> findGCD(1000, 500)
     500
     >>> findGCD(25, 5)
     5
     """
     if (b == 0): 
         return a
     return findGCD(b, a % b)
output:     while b != 0:
          a, b = b, a % b
      return a