input: Write a function to find the greatest common divisor (GCD) of two numbers using the Euclidean algorithm. The function should take two integers as input and return their GCD.
  def findGCD(a, b): 
     if (b == 0): 
         return a
     return findGCD(b, a % b)
  
  assert findGCD(1000, 500) == 500
  assert findGCD(15, 25) == 5
  assert findGCD(21, 14) == 7
  assert findGCD(8, 12) == 4
  assert findGCD(0, 5) == 5
output: def findGCD(a, b): 
     if (b == 0): 
         return a
     return findGCD(b, a % b)