input: Write a function to find the GCD of two numbers using the Euclidean algorithm. If either of the numbers is 0, return the other number as the GCD.
  assert findGCD(1000, 500)==500
  assert findGCD(14, 28)==14
  assert findGCD(0, 9)==9
  assert findGCD(9, 0)==9
  assert findGCD(7, 13)==1
output: def findGCD(a, b):
      while b != 0:
          a, b = b, a % b
      return a