import kotlin.math.ceil

fun main(args: Array<String>) {
    //val (h, w)= Pair(1L, 4L)
    val (h, w)= readLine()!!.split(" ").map { it.toLong() }

    if (h == 1L || w == 1L) {
        println("1")
        return
    }

    val answer = ceil((h * w).toDouble() / 2).toLong()

    println("$answer")
}
