main = do
 [h,w] <- map (read::String->Int) .words <$> getLine
 if h < w then print $  h * (w `div` 2) + ceiling((fromIntegral h)/2) * (w `mod` 2)
 else print $  w * (h `div` 2) + ceiling((fromIntegral w)/2) * (h `mod` 2)