fun main(args: Array<String>){

            val list = readLine()!!.split(" ").map { it.toLong()}
            val H:Long=list[0]
            val W:Long=list[1]
            if(H % 2==1L && W % 2==1L){
                println(((W *H)+1)/2)
            }
            else{
                println((H*W)/2)
            }
     
    }