import Data.List
import Data.Maybe

split :: Char -> String -> [String]
split c s = let (a,b) = splitAt ((fromJust . elemIndex c) s) s
             in [a, tail b]

solve :: [[[Int]]] -> Int
solve [] = 0
solve ([[h1,m1],[h2,m2]]:xs) = mm + solve xs
  where
    s = h1 * 60 + m1
    t = h2 * 60 + m2
    mm = if s <= t then t - s else 1440 - s + t

main :: IO ()
main = do
    n <- readLn :: IO Int
    xs <- map (map (map read . split ':') . words) . lines <$> getContents :: IO [[[Int]]]
    print $ solve xs