"""
https://en.wikipedia.org/wiki/Check_digit#Algorithms
"""


def get_check_digit(barcode: int) -> int:
 """
 Returns the last digit of barcode by excluding the last digit first
 and then computing to reach the actual last digit from the remaining
 12 digits.

 >>> get_check_digit(8718452538119)
 9
 >>> get_check_digit(87184523)
 5
 >>> get_check_digit(87193425381086)
 9
 >>> [get_check_digit(x) for x in range(0, 100, 10)]
 [0, 7, 4, 1, 8, 5, 2, 9, 6, 3]
 """
 barcode //= 10 # exclude the last digit
 checker = False
 s = 0

 # extract and check each digit
 while barcode != 0:
 mult = 1 if checker else 3
 s += mult * (barcode % 10)
 barcode //= 10
 checker = not checker

 return (10 - (s % 10)) % 10


def is_valid(barcode: int) -> bool:
 """
 Checks for length of barcode and last-digit
 Returns boolean value of validity of barcode

 >>> is_valid(8718452538119)
 True
 >>> is_valid(87184525)
 False
 >>> is_valid(87193425381089)
 False
 >>> is_valid(0)
 False
 >>> is_valid(dwefgiweuf)
 Traceback (most recent call last):
 ...
 NameError: name 'dwefgiweuf' is not defined
 """
 return len(str(barcode)) == 13 and get_check_digit(barcode) == barcode % 10


def get_barcode(barcode: str) -> int:
 """
 Returns the barcode as an integer

 >>> get_barcode("8718452538119")
 8718452538119
 >>> get_barcode("dwefgiweuf")
 Traceback (most recent call last):
 ...
 ValueError: Barcode 'dwefgiweuf' has alphabetic characters.
 """
 if str(barcode).isalpha():
 msg = f"Barcode '{barcode}' has alphabetic characters."
 raise ValueError(msg)
 elif int(barcode) < 0:
 raise ValueError("The entered barcode has a negative value. Try again.")
 else:
 return int(barcode)


if __name__ == "__main__":
 import doctest

 doctest.testmod()
 """
 Enter a barcode.

 """
 barcode = get_barcode(input("Barcode: ").strip())

 if is_valid(barcode):
 print(f"'{barcode}' is a valid barcode.")
 else:
 print(f"'{barcode}' is NOT a valid barcode.")