import Data.List.Split (splitOn)

toMinutes :: String -> Int
toMinutes = (\(h : m : _) -> h * 60 + m) . map read . splitOn ":"

getSleep :: [String] -> Int
getSleep (st : en : _)
    | st' > en' = en' + 24 * 60 - st'
    | otherwise = en' - st'
    where
        [st', en'] = map toMinutes [st, en]

main :: IO ()
main = getLine >> getContents >>= print . sum . map getSleep . map words . lines