import Data.List.Split

toInt :: String -> Int
toInt = read :: String -> Int

countReachableSquares :: Int -> Int -> Int
countReachableSquares h w
  | h == 1 = 1
  | w == 1 = 1
  | otherwise = ceiling (fromIntegral (h * w) / 2)

main = do
  s <- getLine
  let l = splitOn " " s 
  let h = toInt (l!!0)
  let w = toInt (l!!1)
  putStrLn $ show $ countReachableSquares h w
