main = do
	[r, c] <- getLine >>= return . map read . words
	print $
		if r == c
			then if mod r 2 == 0
				then (div r 2) ^ 2 - 1
				else (div r 2) ^ 2 + (div r 2)
			else if mod r 2 == 0
				then if mod c 2 == 0
					then ((div r 2) * (div c 2)) * 2 - 1
					else (div r 2) * c - 1
				else if mod c 2 == 0
					then r * (div c 2) - 1
					else ((div r 2) * (div c 2)) * 2 + (div r 2) + (div c 2)