{-# LANGUAGE BangPatterns #-}
import Control.Arrow
import Control.Monad
import Control.Monad.Fix
import Data.Int
import Data.Foldable
import qualified Data.Vector as V
import qualified Data.Vector.Unboxed as VU
import qualified Data.Vector.Unboxed.Mutable as VUM
import qualified Data.ByteString.Char8 as B
import Data.ByteString.Internal (accursedUnutterablePerformIO)
import Debug.Trace

solve :: Int -> VU.Vector (Int, Int) -> Int
solve !n !abn = fst
  $ VU.foldl' (\(!a, !b) (!an, !bn) -> (an - b, bn - a)) (0, 0) abn

main = do
  let readInt :: Integral a => B.ByteString -> Maybe (a, B.ByteString)
      readInt = fmap (first fromIntegral . second B.tail) . B.readInt

  n   <- (\vec -> (vec VU.! 0)) . VU.unfoldrN 1 readInt <$> B.getLine
  abn <-
    VU.replicateM n
    $   (\vec -> (vec VU.! 0, vec VU.! 1))
    .   VU.unfoldrN 2 readInt
    <$> B.getLine
  print $ solve n abn
