```go
package main

import (
	"fmt"
)

func main() {
	var n, m int
	fmt.Scan(&n, &m)
	
	if n > m {
		n, m = m, n
	}
	
	if n == 1 {
		fmt.Println(n * m)
	} else if n == 2 {
		r := m % 4
		add := 0
		if r == 1 {
			add = 2
		} else if r >= 2 {
			add = 4
		}
		fmt.Println(4*(m/4) + add)
	} else {
		fmt.Println((n*m + 1) / 2)
	}
}
```