import java.util.*;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        System.out.println((int)Math.ceil(n / (2.0 * d + 1.0)));
        sc.close();

    }

} import java.util.*; util.* java public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        System.out.println((int)Math.ceil(n / (2.0 * d + 1.0)));
        sc.close();

    }

} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        System.out.println((int)Math.ceil(n / (2.0 * d + 1.0)));
        sc.close();

    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        System.out.println((int)Math.ceil(n / (2.0 * d + 1.0)));
        sc.close();

    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int d = sc.nextInt(); d sc.nextInt() sc.nextInt sc System.out.println((int)Math.ceil(n / (2.0 * d + 1.0))) System.out.println System.out System System.out (int)Math.ceil(n / (2.0 * d + 1.0)) Math.ceil Math n / (2.0 * d + 1.0) n (2.0 * d + 1.0) 2.0 * d 2.0 d 1.0 sc.close() sc.close sc String[] args args public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        System.out.println((int)Math.ceil(n / (2.0 * d + 1.0)));
        sc.close();

    }

} public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        System.out.println((int)Math.ceil(n / (2.0 * d + 1.0)));
        sc.close();

    }

} Main
import java.util.*;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int d = sc.nextInt();
        System.out.println((int)Math.ceil(n / (2.0 * d + 1.0)));
        sc.close();

    }

}
