import           Control.Monad
import qualified Data.ByteString.Char8 as BS
import           Data.Maybe

readInteger = fst . fromJust . BS.readInteger
readIntegerList = map readInteger . BS.words
getInteger = readInteger <$> BS.getLine
getIntegerList = readIntegerList <$> BS.getLine

main = do
  [h, w] <- getIntegerList
  print $ (h*w+1) `div` 2