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