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

readInt = fst . fromJust . BS.readInt
readIntList = map readInt . BS.words
getInt = readInt <$> BS.getLine
getIntList = readIntList <$> BS.getLine

main = do
    [h, w] <- getIntList
    let hd = h `div` 2
    let hm = h `mod` 2
    let wd = w `div` 2
    let wm = w `mod` 2
    print $ hd * w + hm * (wd + wm)