{-# LANGUAGE FlexibleContexts, OverloadedStrings #-}
import Control.Applicative
import Control.Monad
import qualified Data.ByteString.Char8 as B
import Data.Maybe (fromJust)
import Data.List
import Text.Printf
import Debug.Trace

main = do
  [w] <- getInts
  [h] <- getInts
  [n] <- getInts
  xxs <- replicateM (fromInteger n) getInts
  let xl = fromIntegral $ length $ nub $ map head xxs
  let yl = fromIntegral $ length $ nub $ map (head . tail) xxs
  print $ xl * h + yl * w - xl * yl - n

-- util
getInts :: IO [Integer]
getInts = map (fst . fromJust . B.readInteger) . B.words <$> B.getLine

substr :: Int -> Int -> B.ByteString -> B.ByteString
substr b l s = B.take l $ B.drop b s