import Control.Monad
import Data.List

main = do
  n <- readLn
  ws <- replicateM n $ words <$> getLine
  
  let ws' = map (\[x, y] -> (getMin x, getMin y)) ws
  
  print $ sum $ map sleep ws'

getMin time = (read h) * 60 + (read m)
  where (h,(':':m)) = break (== ':') time

sleep (minS, minE) = if t < 0 then 60 * 24 + t else t
  where t = minE - minS