input: Write a function to find the GCD of two numbers. Use the Euclidean algorithm to find the greatest common divisor. The function should return the GCD of the two input numbers.
  
  def findGCD(a, b):
     if (b == 0):
         return a
     return findGCD(b, a % b)
  
  assert findGCD(1000, 500) == 500
  assert findGCD(12, 8) == 4
  assert findGCD(27, 18) == 9
  assert findGCD(17, 5) == 1
  assert findGCD(0, 0) == 0
output: def findGCD(a, b):
     if (b == 0):
         return a
     return findGCD(b, a % b)