fun main(args:Array<String>){
    val line = readLine()!!.split(" ").map { it.toLong() }
    val h = line[0]
    val w = line[1]
    if(h==1L||w==1L){
        println(1)
    }else {
        if (h * w % 2 == 0L) println(h * w / 2) else println(h * w / 2 + 1)
    }
}