import Control.Monad
import Data.Maybe
import qualified Data.ByteString.Char8 as B

rInt :: B.ByteString -> Int
rInt = fst . fromJust . B.readInt

sleep [[h1, m1], [h2, m2]] t = (h2' * 60 + m2) - (h1 * 60 + m1) + t
    where
        h2' | h2 < h1   = h2 + 24
            | otherwise = h2

main = do
    n <- readLn
    times <- map (map (map rInt . (B.split ':')) . B.words) <$> replicateM n B.getLine
    print $ foldr sleep 0 times