input: Write a python function to find the greatest common divisor (GCD) of two numbers using recursion.
  assert findGCD(1000, 500) == 500
  assert findGCD(54, 24) == 6
  assert findGCD(48, 18) == 6
output: def findGCD(a, b):
      if b == 0:
          return a
      else:
          return findGCD(b, a % b)