import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {

    public static void main(String[] args) throws Exception {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            String[] array = reader.readLine().split(" ");
            int N = Integer.parseInt(array[0]);
            int D = Integer.parseInt(array[1]);

            int ret = N / (D * 2 + 1);
            if (N % (D * 2 + 1) != 0) {
                ret++;
            }

            System.out.println(ret);
        }
    }

} import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io public class Main {

    public static void main(String[] args) throws Exception {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            String[] array = reader.readLine().split(" ");
            int N = Integer.parseInt(array[0]);
            int D = Integer.parseInt(array[1]);

            int ret = N / (D * 2 + 1);
            if (N % (D * 2 + 1) != 0) {
                ret++;
            }

            System.out.println(ret);
        }
    }

} Main public static void main(String[] args) throws Exception {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            String[] array = reader.readLine().split(" ");
            int N = Integer.parseInt(array[0]);
            int D = Integer.parseInt(array[1]);

            int ret = N / (D * 2 + 1);
            if (N % (D * 2 + 1) != 0) {
                ret++;
            }

            System.out.println(ret);
        }
    } main {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            String[] array = reader.readLine().split(" ");
            int N = Integer.parseInt(array[0]);
            int D = Integer.parseInt(array[1]);

            int ret = N / (D * 2 + 1);
            if (N % (D * 2 + 1) != 0) {
                ret++;
            }

            System.out.println(ret);
        }
    } try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            String[] array = reader.readLine().split(" ");
            int N = Integer.parseInt(array[0]);
            int D = Integer.parseInt(array[1]);

            int ret = N / (D * 2 + 1);
            if (N % (D * 2 + 1) != 0) {
                ret++;
            }

            System.out.println(ret);
        } {
            String[] array = reader.readLine().split(" ");
            int N = Integer.parseInt(array[0]);
            int D = Integer.parseInt(array[1]);

            int ret = N / (D * 2 + 1);
            if (N % (D * 2 + 1) != 0) {
                ret++;
            }

            System.out.println(ret);
        } BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)) BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)) new BufferedReader(new InputStreamReader(System.in)) String[] array = reader.readLine().split(" "); array reader.readLine().split(" ") reader.readLine().split reader.readLine() reader.readLine reader " " int N = Integer.parseInt(array[0]); N Integer.parseInt(array[0]) Integer.parseInt Integer array[0] array 0 int D = Integer.parseInt(array[1]); D Integer.parseInt(array[1]) Integer.parseInt Integer array[1] array 1 int ret = N / (D * 2 + 1); ret N / (D * 2 + 1) N (D * 2 + 1) D * 2 D 2 1 if (N % (D * 2 + 1) != 0) {
                ret++;
            } N % (D * 2 + 1) != 0 N % (D * 2 + 1) N (D * 2 + 1) D * 2 D 2 1 0 {
                ret++;
            } ret++ ret System.out.println(ret) System.out.println System.out System System.out ret String[] args args public class Main {

    public static void main(String[] args) throws Exception {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            String[] array = reader.readLine().split(" ");
            int N = Integer.parseInt(array[0]);
            int D = Integer.parseInt(array[1]);

            int ret = N / (D * 2 + 1);
            if (N % (D * 2 + 1) != 0) {
                ret++;
            }

            System.out.println(ret);
        }
    }

} public class Main {

    public static void main(String[] args) throws Exception {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            String[] array = reader.readLine().split(" ");
            int N = Integer.parseInt(array[0]);
            int D = Integer.parseInt(array[1]);

            int ret = N / (D * 2 + 1);
            if (N % (D * 2 + 1) != 0) {
                ret++;
            }

            System.out.println(ret);
        }
    }

} Main
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {

    public static void main(String[] args) throws Exception {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            String[] array = reader.readLine().split(" ");
            int N = Integer.parseInt(array[0]);
            int D = Integer.parseInt(array[1]);

            int ret = N / (D * 2 + 1);
            if (N % (D * 2 + 1) != 0) {
                ret++;
            }

            System.out.println(ret);
        }
    }

}
