import Data.List.Split (splitOn)

solve :: [Int] -> Int
solve [] = 0
solve xs@(x:_) = x + solve (getDifferences xs)
  where
    getDifferences = zipWith (-) <*> tail

main :: IO ()
main = print . sum . map solveLine . lines =<< readFile "data.txt"
  where
    solveLine = solve . reverse . map read . splitOn " "