local h, w = io.read("*n", "*n")
if h == 1 then
  print(1)
elseif w == 1 then
  print(1)
elseif h % 2 == 0 or w % 2 == 0 then
  print((h * w) // 2)
else
  local a = w // 2
  local b = h // 2
  print(a * b + (a + 1) * (b + 1))
end
