fun main(args: Array<String>){
    var (a,b)=readLine()!!.split(" ").map(String::toInt)
	val c = a / b 
	if (((a % b) != 0) || (((a / b) % 2) != 0)) {
        println((a / 2) * b)
    } else {
        println(0)
    }
}