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

readInt = fromIntegral . fst . fromJust . BS.readInteger
readIntList = map readInt . BS.words

getInt = readInt <$> BS.getLine
getIntList = readIntList <$> BS.getLine

main = do
  [h, w] <- getIntList
  let s = h * w
  let d = s `div` 2
  let m = s `mod` 2
  if m == 0 then
    print d
  else
    print $ d + 1