object Main extends App {
  val in = scala.io.Source.stdin.getLines.toSeq
  val ls = in.map(_.split(' ').map(_.toLong))
  val H = ls(0)(0)
  val W = ls(0)(1)
  
  if(H == 1 || W == 1) println(1)
  else{
    val ret = (H * W + 1) / 2
    println(ret)
  }
}
