import Control.Applicative
import Control.Monad
import Data.List
import Data.Monoid
import Data.Tuple

time h m = 60 * h + m

f [x, y] = (parse y - parse x) `mod` time 24 0
  where
    parse = uncurry time . swap . fmap read . swap . fmap (read . tail) . span (/=':')

main = readLn >>= flip replicateM (words <$> getLine) >>= print . sum . map f