import java.util.*;

public class Main {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String[] values = scanner.nextLine().split(" ");
        int N = Integer.parseInt(values[0]);
        int D = Integer.parseInt(values[1]);

        int count = 0;
        while (true) {

            N = N - (2 * D + 1);

            if (N > 0) {
                count++;
            } else {
                count++;
                break;
            }

        }

        System.out.println(count);

        scanner.close();

    }

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

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String[] values = scanner.nextLine().split(" ");
        int N = Integer.parseInt(values[0]);
        int D = Integer.parseInt(values[1]);

        int count = 0;
        while (true) {

            N = N - (2 * D + 1);

            if (N > 0) {
                count++;
            } else {
                count++;
                break;
            }

        }

        System.out.println(count);

        scanner.close();

    }

} Main public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String[] values = scanner.nextLine().split(" ");
        int N = Integer.parseInt(values[0]);
        int D = Integer.parseInt(values[1]);

        int count = 0;
        while (true) {

            N = N - (2 * D + 1);

            if (N > 0) {
                count++;
            } else {
                count++;
                break;
            }

        }

        System.out.println(count);

        scanner.close();

    } main {

        Scanner scanner = new Scanner(System.in);

        String[] values = scanner.nextLine().split(" ");
        int N = Integer.parseInt(values[0]);
        int D = Integer.parseInt(values[1]);

        int count = 0;
        while (true) {

            N = N - (2 * D + 1);

            if (N > 0) {
                count++;
            } else {
                count++;
                break;
            }

        }

        System.out.println(count);

        scanner.close();

    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) String[] values = scanner.nextLine().split(" "); values scanner.nextLine().split(" ") scanner.nextLine().split scanner.nextLine() scanner.nextLine scanner " " int N = Integer.parseInt(values[0]); N Integer.parseInt(values[0]) Integer.parseInt Integer values[0] values 0 int D = Integer.parseInt(values[1]); D Integer.parseInt(values[1]) Integer.parseInt Integer values[1] values 1 int count = 0; count 0 while (true) {

            N = N - (2 * D + 1);

            if (N > 0) {
                count++;
            } else {
                count++;
                break;
            }

        } true {

            N = N - (2 * D + 1);

            if (N > 0) {
                count++;
            } else {
                count++;
                break;
            }

        } N = N - (2 * D + 1) N N - (2 * D + 1) N (2 * D + 1) 2 * D 2 D 1 if (N > 0) {
                count++;
            } else {
                count++;
                break;
            } N > 0 N 0 {
                count++;
            } count++ count {
                count++;
                break;
            } count++ count break; System.out.println(count) System.out.println System.out System System.out count scanner.close() scanner.close scanner String[] args args public class Main {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String[] values = scanner.nextLine().split(" ");
        int N = Integer.parseInt(values[0]);
        int D = Integer.parseInt(values[1]);

        int count = 0;
        while (true) {

            N = N - (2 * D + 1);

            if (N > 0) {
                count++;
            } else {
                count++;
                break;
            }

        }

        System.out.println(count);

        scanner.close();

    }

} public class Main {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String[] values = scanner.nextLine().split(" ");
        int N = Integer.parseInt(values[0]);
        int D = Integer.parseInt(values[1]);

        int count = 0;
        while (true) {

            N = N - (2 * D + 1);

            if (N > 0) {
                count++;
            } else {
                count++;
                break;
            }

        }

        System.out.println(count);

        scanner.close();

    }

} Main
import java.util.*;

public class Main {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        String[] values = scanner.nextLine().split(" ");
        int N = Integer.parseInt(values[0]);
        int D = Integer.parseInt(values[1]);

        int count = 0;
        while (true) {

            N = N - (2 * D + 1);

            if (N > 0) {
                count++;
            } else {
                count++;
                break;
            }

        }

        System.out.println(count);

        scanner.close();

    }

}
