n = input('Input your credit card number: ')

def legitcheck(n):
    grand_summa = 0
    if len(n) == 13 or len(n) == 16:

        for i in range(len(n) - 2, -1, -2):
            s = int(n[i]) * 2
            if s > 9:
                grand_summa += 1 + s % 10
            else:
                grand_summa+= s
        for i in range(len(n) - 1, -1, -2):
            grand_summa += int(n[i])

        if grand_summa % 10 == 0:
            print('Your card is valid')
        else:
            print('**fake card is being detected**')
    else:
        print("*invalid card*")
legitcheck(n)