import java.util.Scanner;

public class A000063 {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		int l = s.nextInt();
		int k = s.nextInt();
		s.close();
		int a = 1;
		while(l-2*k*a>0) {
			a++;
		}
		System.out.println(k*(a-1));
	}

}