func main()
	var r: int :: cui@inputInt()
	var c: int :: cui@inputInt()
	var ans: int :: 0
	if(r = c)
		do ans :: (r * c + 3) / 4
	else
		do ans :: (r * c + 1) / 2
	end if
	do ans :- 1
	do cui@print("\{ans}\n")
end func