package Yukicoder

/**
 * Created by hichikawa on 2015/11/02.
 */
fun main(args: Array<String>) {
    fun readLineLongArray() : List<Long> {
        val str = readLine() as String
        val arrStr = str.split(" ")
        val ret = arrStr.map { it.toLong() }
        return ret
    }
    fun readLineLong() : Long {
        val str = readLine() as String
        return str.toLong()
    }
    val inputNum = readLineLongArray()
    val pokeyLen = inputNum[0]
    val eatLen = inputNum[1]
    val eatLenTwo = eatLen * 2
    if (pokeyLen / eatLenTwo * eatLenTwo - pokeyLen == 0.toLong()) {
        println(pokeyLen / eatLenTwo * eatLen - eatLen)
    } else {
        println(pokeyLen / eatLenTwo * eatLen)
    }
}