import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int L = sc.nextInt();
    int K = sc.nextInt();
    int num = (L + 2 * K - 1) / (2 * K) - 1;
    System.out.println(num * K);
  }
}