countCells :: Int -> Int -> Int
countCells 1 _ = 1
countCells _ 1 = 1
countCells h w =
  if h `mod` 2 == 0
    then w * (h `div` 2)
    else w * (h `div` 2) + w `div` 2
       + if w `mod` 2 == 0 then 0 else 1

main :: IO ()
main = do
  [h, w] <- map read . words <$> getLine
  print $ countCells h w
