package main

import "fmt"

func main() {

	var H, W int

	fmt.Scan(&H, &W)

	prod := H * W
	if H < 2 || W < 2 {
		fmt.Println(1)
	} else if prod%2 == 0 {
		fmt.Println(prod / 2)
	} else {
		fmt.Println(prod/2 + 1)
	}

}
