#!/usr/bin/env runhaskell
import Data.ByteString.Lazy.Char8 as BS hiding (filter,take,concat,map,drop,length)
import Data.Char

main = validate_check_digits "4910099710741"
validate_check_digits :: [Char] -> IO ()
validate_check_digits digits = do
  digits <- readF
  putStrLn show $ validate_check_even_digits digits * 3 + validate_check_odd_digits digits

validate_check_even_digits :: [Char] -> Int
validate_check_even_digits [] = 0
validate_check_even_digits (x1:(_:(x2:(_:xs)))) = (digitToInt x1) + (digitToInt x2) + validate_check_even_digits xs

validate_check_odd_digits :: [Char] -> Int
validate_check_odd_digits [] = 0
validate_check_odd_digits (_:odd_digits) = validate_check_even_digits odd_digits

readF :: String -> IO BS.ByteString
readF "-" = BS.getContents
readF f   = BS.readFile f