import           Data.List.Split (splitOn)

lineSafe :: [Int] -> Bool
lineSafe [] = True
lineSafe l@(_:xs) = (all (> 0) diffs || all (< 0) diffs) && all validItem diffs
  where
    diffs = zipWith (-) xs l

    validItem x = x /= 0 && abs x <= 3

main :: IO ()
main = print . length . filter testLine . lines =<< readFile "data.txt"
  where
    testLine = lineSafe . map read . splitOn " "