import java.math.BigDecimal
import java.math.RoundingMode
 
fun main(args: Array<String>) {
    val(h, w) = readLine()!!.split(" ").map(String::toLong)
    if(h == 1L || w == 1L) {
      println(1)
      return
    }
    val s = BigDecimal.valueOf(h).multiply(BigDecimal.valueOf(w)).add(BigDecimal.ONE)
    val a = s.divide(BigDecimal.valueOf(2), 0, RoundingMode.FLOOR)
    println(a.toPlainString())
}
