object Main extends App {
  val in = new java.util.Scanner(System.in)
  val H, W = in.nextLong
  val n =
    if (H == 1 || W == 1) 1
    else H * W / 2 + (if (H % 2 == 0 || W % 2 == 0) 0 else 1)
  println(n)
}