input: def findGCD(a, b):
      """ 
      Calculates the greatest common divisor (GCD) of two numbers using the Euclidean algorithm.
      >>> findGCD(1000, 500)
      500
      >>> findGCD(23, 17)
      1
      >>> findGCD(15, 25)
      5
      """
      if (b == 0):
          return a
      return findGCD(b, a % b)
output:     if (b == 0):
          return a
      return findGCD(b, a % b)