import scala.io.StdIn._
import java.util.Scanner

object Main {
  def main(args: Array[String]) = {
    val s = new Scanner(System.in)
    val H = s.nextLong
    val W = s.nextLong
    if (H == 1 || W == 1) {
      println("1")
    } else {
      println((H * W + 1) / 2)
    }
  }
}