import java.util.Scanner

object pokky {
  def main(args: Array[String]): Unit = {
    val sc = new Scanner(System.in)
    var l = sc.nextInt
    val k = sc.nextInt
    var y = 0
    var count = 0

    while(l > 0) {
      l = l - 2 * k
      if (l <= 0) {
        y = k * count
      }
      count += 1
    }
    println(y)
  }
}