import java.util.Scanner;

public class PockyGame{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int L = sc.nextInt();
        int K = sc.nextInt();

        int n = 0;
        if(L%(K*2) == 0){
            n = L/(K*2);
        }else{
            n = L/(K*2)+1;
        }
        System.out.println(K*(n-1));

    }
}