input: Write a function to find the GCD of two numbers. If one of the numbers is zero, return the other number.
  
  def findGCD(a, b): 
     if (b == 0): 
         return a
     return findGCD(b, a % b)
  
  assert findGCD(1000, 500) == 500
  assert findGCD(8, 12) == 4
  assert findGCD(0, 7) == 7
  assert findGCD(15, 0) == 15
  assert findGCD(15, 5) == 5
output: def findGCD(a, b): 
     if (b == 0): 
         return a
     return findGCD(b, a % b)