-- https://adventofcode.com/2024/day/1 (mit dank an flo)

import Data.String

gather : IO (List (Int, Int))
gather = do
  line <- getLine
  case map parsePositive (words line) of
    [Just left, Just right] => do
    	  rest <- gather
    	  pure ((left, right) :: rest)
    _ => pure []

solve : List (Int, Int) -> Int
solve stuff =
  let left = sort $ map fst stuff
      right = sort $ map snd stuff
  in sum $ zipWith (abs .: (-)) left right

main : IO ()
main = gather >>= printLn . solve