import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.PrintWriter;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) throws Exception {
        try (BufferedInputStream in = new BufferedInputStream(System.in);
             PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out))) {

            Scanner sc = new Scanner(in);

            // 12:05-

            int n = sc.nextInt();
            int d = sc.nextInt();

            int range = 2 * d + 1;
            out.println((n + range - 1) / range);
        }
    }

} import java.io.BufferedInputStream; BufferedInputStream java.io import java.io.BufferedOutputStream; BufferedOutputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) throws Exception {
        try (BufferedInputStream in = new BufferedInputStream(System.in);
             PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out))) {

            Scanner sc = new Scanner(in);

            // 12:05-

            int n = sc.nextInt();
            int d = sc.nextInt();

            int range = 2 * d + 1;
            out.println((n + range - 1) / range);
        }
    }

} Main public static void main(String[] args) throws Exception {
        try (BufferedInputStream in = new BufferedInputStream(System.in);
             PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out))) {

            Scanner sc = new Scanner(in);

            // 12:05-

            int n = sc.nextInt();
            int d = sc.nextInt();

            int range = 2 * d + 1;
            out.println((n + range - 1) / range);
        }
    } main {
        try (BufferedInputStream in = new BufferedInputStream(System.in);
             PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out))) {

            Scanner sc = new Scanner(in);

            // 12:05-

            int n = sc.nextInt();
            int d = sc.nextInt();

            int range = 2 * d + 1;
            out.println((n + range - 1) / range);
        }
    } try (BufferedInputStream in = new BufferedInputStream(System.in);
             PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out))) {

            Scanner sc = new Scanner(in);

            // 12:05-

            int n = sc.nextInt();
            int d = sc.nextInt();

            int range = 2 * d + 1;
            out.println((n + range - 1) / range);
        } {

            Scanner sc = new Scanner(in);

            // 12:05-

            int n = sc.nextInt();
            int d = sc.nextInt();

            int range = 2 * d + 1;
            out.println((n + range - 1) / range);
        } BufferedInputStream in = new BufferedInputStream(System.in) BufferedInputStream in = new BufferedInputStream(System.in) new BufferedInputStream(System.in) PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out)) PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out)) new PrintWriter(new BufferedOutputStream(System.out)) Scanner sc = new Scanner(in); sc new Scanner(in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int d = sc.nextInt(); d sc.nextInt() sc.nextInt sc int range = 2 * d + 1; range 2 * d + 1 2 * d 2 d 1 out.println((n + range - 1) / range) out.println out (n + range - 1) / range (n + range - 1) n + range n range 1 range String[] args args public class Main {

    public static void main(String[] args) throws Exception {
        try (BufferedInputStream in = new BufferedInputStream(System.in);
             PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out))) {

            Scanner sc = new Scanner(in);

            // 12:05-

            int n = sc.nextInt();
            int d = sc.nextInt();

            int range = 2 * d + 1;
            out.println((n + range - 1) / range);
        }
    }

} public class Main {

    public static void main(String[] args) throws Exception {
        try (BufferedInputStream in = new BufferedInputStream(System.in);
             PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out))) {

            Scanner sc = new Scanner(in);

            // 12:05-

            int n = sc.nextInt();
            int d = sc.nextInt();

            int range = 2 * d + 1;
            out.println((n + range - 1) / range);
        }
    }

} Main
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.PrintWriter;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) throws Exception {
        try (BufferedInputStream in = new BufferedInputStream(System.in);
             PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out))) {

            Scanner sc = new Scanner(in);

            // 12:05-

            int n = sc.nextInt();
            int d = sc.nextInt();

            int range = 2 * d + 1;
            out.println((n + range - 1) / range);
        }
    }

}
