import Control.Monad

main = do
 n <- readLn
 hms <- map (map readTime . words) <$> replicateM n getLine
 print $ sum (map hours hms)

readTime s = 60 * read h + read m
 where (h,(':':m)) = break (==':') s

hours [t1,t2] = mod (t2 - t1) 1440