import java.util.Scanner;

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

        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int D = scanner.nextInt();
        int area = 2 * D + 1;
        if (area > N) {
            System.out.println("1");
        } else if (N % area == 0){
            System.out.println(N / area);
        } else {
            System.out.println(N / area + 1);
        }
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int D = scanner.nextInt();
        int area = 2 * D + 1;
        if (area > N) {
            System.out.println("1");
        } else if (N % area == 0){
            System.out.println(N / area);
        } else {
            System.out.println(N / area + 1);
        }
    }
} Main public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int D = scanner.nextInt();
        int area = 2 * D + 1;
        if (area > N) {
            System.out.println("1");
        } else if (N % area == 0){
            System.out.println(N / area);
        } else {
            System.out.println(N / area + 1);
        }
    } main {

        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int D = scanner.nextInt();
        int area = 2 * D + 1;
        if (area > N) {
            System.out.println("1");
        } else if (N % area == 0){
            System.out.println(N / area);
        } else {
            System.out.println(N / area + 1);
        }
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int N = scanner.nextInt(); N scanner.nextInt() scanner.nextInt scanner int D = scanner.nextInt(); D scanner.nextInt() scanner.nextInt scanner int area = 2 * D + 1; area 2 * D + 1 2 * D 2 D 1 if (area > N) {
            System.out.println("1");
        } else if (N % area == 0){
            System.out.println(N / area);
        } else {
            System.out.println(N / area + 1);
        } area > N area N {
            System.out.println("1");
        } System.out.println("1") System.out.println System.out System System.out "1" if (N % area == 0){
            System.out.println(N / area);
        } else {
            System.out.println(N / area + 1);
        } N % area == 0 N % area N area 0 {
            System.out.println(N / area);
        } System.out.println(N / area) System.out.println System.out System System.out N / area N area {
            System.out.println(N / area + 1);
        } System.out.println(N / area + 1) System.out.println System.out System System.out N / area + 1 N / area N area 1 String[] args args public class Main {
    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int D = scanner.nextInt();
        int area = 2 * D + 1;
        if (area > N) {
            System.out.println("1");
        } else if (N % area == 0){
            System.out.println(N / area);
        } else {
            System.out.println(N / area + 1);
        }
    }
} public class Main {
    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int D = scanner.nextInt();
        int area = 2 * D + 1;
        if (area > N) {
            System.out.println("1");
        } else if (N % area == 0){
            System.out.println(N / area);
        } else {
            System.out.println(N / area + 1);
        }
    }
} Main
import java.util.Scanner;

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

        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int D = scanner.nextInt();
        int area = 2 * D + 1;
        if (area > N) {
            System.out.println("1");
        } else if (N % area == 0){
            System.out.println(N / area);
        } else {
            System.out.println(N / area + 1);
        }
    }
}