input: Write a function to find the GCD of two numbers using the Euclidean algorithm.
  def findGCD(a, b):
      if b == 0:
          return a
      return findGCD(b, a % b)
  
  assert findGCD(1000, 500) == 500
  assert findGCD(48, 18) == 6
  assert findGCD(15, 10) == 5
  assert findGCD(7, 5) == 1
  assert findGCD(0, 0) == 0
output: def findGCD(a, b):
      if b == 0:
          return a
      return findGCD(b, a % b)