solve :: Int -> Int -> Int
solve h w =
  case (h `mod` 2 == 0, w `mod` 2 == 0) of
    (False, False) -> 
      let h1 = h `div` 2
          h2 = (h + 1) `div` 2
          w1 = w `div` 2
          w2 = (w + 1) `div` 2
      in
        h1 * w1 + h2 * w2
    (False, True) -> 
      (w `div` 2) * h
    (True, False) -> 
      (h `div` 2) * w
    (True, True) -> 
      (h `div` 2) * w

main = do
  [h, w] <- map read . words <$> getLine
  print $ solve h w