import java.util.Scanner;

/**
 * Main
 */
public class Main {

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

        double N = sc.nextInt();
        double D = sc.nextInt();

        double watch = 1 + D*2;

        double answer = Math.ceil(N/watch);

        // System.out.println(N);
        // System.out.println(watch);
        System.out.println((int)answer);


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

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

        double N = sc.nextInt();
        double D = sc.nextInt();

        double watch = 1 + D*2;

        double answer = Math.ceil(N/watch);

        // System.out.println(N);
        // System.out.println(watch);
        System.out.println((int)answer);


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

        double N = sc.nextInt();
        double D = sc.nextInt();

        double watch = 1 + D*2;

        double answer = Math.ceil(N/watch);

        // System.out.println(N);
        // System.out.println(watch);
        System.out.println((int)answer);


    } main {
        Scanner sc = new Scanner(System.in);

        double N = sc.nextInt();
        double D = sc.nextInt();

        double watch = 1 + D*2;

        double answer = Math.ceil(N/watch);

        // System.out.println(N);
        // System.out.println(watch);
        System.out.println((int)answer);


    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double N = sc.nextInt(); N sc.nextInt() sc.nextInt sc double D = sc.nextInt(); D sc.nextInt() sc.nextInt sc double watch = 1 + D*2; watch 1 + D*2 1 D*2 D 2 double answer = Math.ceil(N/watch); answer Math.ceil(N/watch) Math.ceil Math N/watch N watch System.out.println((int)answer) System.out.println System.out System System.out (int)answer String[] args args public class Main {

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

        double N = sc.nextInt();
        double D = sc.nextInt();

        double watch = 1 + D*2;

        double answer = Math.ceil(N/watch);

        // System.out.println(N);
        // System.out.println(watch);
        System.out.println((int)answer);


    }
} public class Main {

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

        double N = sc.nextInt();
        double D = sc.nextInt();

        double watch = 1 + D*2;

        double answer = Math.ceil(N/watch);

        // System.out.println(N);
        // System.out.println(watch);
        System.out.println((int)answer);


    }
} Main
import java.util.Scanner;

/**
 * Main
 */
public class Main {

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

        double N = sc.nextInt();
        double D = sc.nextInt();

        double watch = 1 + D*2;

        double answer = Math.ceil(N/watch);

        // System.out.println(N);
        // System.out.println(watch);
        System.out.println((int)answer);


    }
}