import Foundation

func readInts() -> [Int]{
    return readLine()!.split(separator: " ").map { Int($0)! }
}
func readInt() -> Int {
    return Int(readLine()!)!
}

func main() {
    let hw = readInts()
    let (h, w) = (hw[0], hw[1])
    let multiplied = h * w
    print(multiplied.isMultiple(of: 2) ? multiplied / 2: multiplied / 2 + 1)
}

main()

