h , w = map(int, input().split())
c = 0
if h == 1 or w ==1:
	print(1)
	exit()
 
if w % 2 == 0:
	print(h * w // 2)
	exit()
elif w % 2 == 1:
	if h % 2 == 0:
		print(h * w // 2)
		exit()
	elif h % 2 == 1:
		print((h * w // 2) + 1)
		exit()