input: Write a function to calculate the Greatest Common Divisor (GCD) of two numbers using the Euclidean algorithm. If one of the numbers is 0, it should return the other number as the GCD.
  
  def findGCD(a, b): 
     if (b == 0): 
         return a
     return findGCD(b, a % b)
  
  assert findGCD(1000, 500) == 500
  assert findGCD(14, 21) == 7
  assert findGCD(0, 55) == 55
  assert findGCD(25, 0) == 25
  assert findGCD(12, 18) == 6
output: def findGCD(a, b): 
     if (b == 0): 
         return a
     return findGCD(b, a % b)