class VerifyCreditCard:
    def checkDigits(self, cardNumber):
        l = len(cardNumber)%2
        ls = [2*int(e) if i%2 == l else int(e) for i, e in enumerate(cardNumber)]
        return 'VALID' if sum(map(lambda e: sum(map(int, str(e))), ls))%10 == 0 else 'INVALID'
