import java.util.Scanner;
import java.lang.Math;

    public class Main {
        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            
            int L = sc.nextInt();
            int K = sc.nextInt();
            
            int ans = 0;
            while(L>0){
                L -= 2*K;
                if(L<=0){
                    break;
                }
                ans++;
            }
            System.out.println(ans*K);
            
        }
    }