input: Write a function to calculate the greatest common divisor (GCD) of two given numbers. The function should take two integers as input and return the GCD. If either of the input numbers is zero, the function should return the non-zero number as the GCD.
  assert findGCD(1000, 500)==500
  assert findGCD(60, 48)==12
  assert findGCD(0, 5)==5
  assert findGCD(123, 0)==123
  assert findGCD(15, 25)==5
output: def findGCD(a, b):
      while b != 0:
          a, b = b, a % b
      return a