import qualified Data.IntSet as S

main :: IO ()
main = do
    w <- readLn :: IO Int
    h <- readLn :: IO Int
    n <- readLn :: IO Int
    sk <- map ((\[a,b] -> (a,b)) . (map read . words))
        . lines <$> getContents :: IO [(Int,Int)]
    let w' = S.size . S.fromList $ map fst sk
    let h' = S.size . S.fromList $ map snd sk
    print $ w * h - (w-w') * (h-h') - n