
main = do
  [h, w] <- (map read) . words <$> getLine :: IO [Int]
  print $
    if w `mod` 2 == 0
      then w`div`2 * h
    else
      if h `mod` 2 == 0
            then ((w`div`2)+1)*(h`div`2) + (w`div`2)*(h`div`2)
            else ((w`div`2)+1)*(h`div`2+1) + (w`div`2)*(h`div`2)