import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final int N = sc.nextInt();
        final int D = sc.nextInt();

        System.out.println((int)Math.ceil(N / (D * 2 + 1.0)));
    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final int N = sc.nextInt();
        final int D = sc.nextInt();

        System.out.println((int)Math.ceil(N / (D * 2 + 1.0)));
    }
} Main public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final int N = sc.nextInt();
        final int D = sc.nextInt();

        System.out.println((int)Math.ceil(N / (D * 2 + 1.0)));
    } main {
        final Scanner sc = new Scanner(System.in);

        final int N = sc.nextInt();
        final int D = sc.nextInt();

        System.out.println((int)Math.ceil(N / (D * 2 + 1.0)));
    } final Scanner sc = new Scanner(System.in); sc new Scanner(System.in) final int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc final int D = sc.nextInt(); D sc.nextInt() sc.nextInt sc System.out.println((int)Math.ceil(N / (D * 2 + 1.0))) System.out.println System.out System System.out (int)Math.ceil(N / (D * 2 + 1.0)) Math.ceil Math N / (D * 2 + 1.0) N (D * 2 + 1.0) D * 2 D 2 1.0 String[] args args public class Main {

    public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final int N = sc.nextInt();
        final int D = sc.nextInt();

        System.out.println((int)Math.ceil(N / (D * 2 + 1.0)));
    }
} public class Main {

    public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final int N = sc.nextInt();
        final int D = sc.nextInt();

        System.out.println((int)Math.ceil(N / (D * 2 + 1.0)));
    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final int N = sc.nextInt();
        final int D = sc.nextInt();

        System.out.println((int)Math.ceil(N / (D * 2 + 1.0)));
    }
}
