import scala.math.round

object Main extends App {
  
  val sc = new java.util.Scanner(System.in)
  val H = sc.nextLong()
  val W = sc.nextLong()

  if (H == 1L || W == 1L) {
    println(1)
  } else {
    println(round(H * W / 2))
  }
  
}