import java.util.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    public static void main(String[] args) throws Exception {
        // 入力受取
        BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
        String line1 = input.readLine();

        String[] arr = line1.split(" ");
        int N = Integer.parseInt(arr[0]);
        int D = Integer.parseInt(arr[1]);

        // 1人が見れる本数
        int a = D * 2 + 1;
        // N本を見るために必要な監視員
        int b = N / a;
        if(N % a > 0) b++;

        System.out.println(b);
    }
} import java.util.*; util.* java import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io public class Main {
    public static void main(String[] args) throws Exception {
        // 入力受取
        BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
        String line1 = input.readLine();

        String[] arr = line1.split(" ");
        int N = Integer.parseInt(arr[0]);
        int D = Integer.parseInt(arr[1]);

        // 1人が見れる本数
        int a = D * 2 + 1;
        // N本を見るために必要な監視員
        int b = N / a;
        if(N % a > 0) b++;

        System.out.println(b);
    }
} Main public static void main(String[] args) throws Exception {
        // 入力受取
        BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
        String line1 = input.readLine();

        String[] arr = line1.split(" ");
        int N = Integer.parseInt(arr[0]);
        int D = Integer.parseInt(arr[1]);

        // 1人が見れる本数
        int a = D * 2 + 1;
        // N本を見るために必要な監視員
        int b = N / a;
        if(N % a > 0) b++;

        System.out.println(b);
    } main {
        // 入力受取
        BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
        String line1 = input.readLine();

        String[] arr = line1.split(" ");
        int N = Integer.parseInt(arr[0]);
        int D = Integer.parseInt(arr[1]);

        // 1人が見れる本数
        int a = D * 2 + 1;
        // N本を見るために必要な監視員
        int b = N / a;
        if(N % a > 0) b++;

        System.out.println(b);
    } BufferedReader input = new BufferedReader(new InputStreamReader(System.in)); input new BufferedReader(new InputStreamReader(System.in)) String line1 = input.readLine(); line1 input.readLine() input.readLine input String[] arr = line1.split(" "); arr line1.split(" ") line1.split line1 " " int N = Integer.parseInt(arr[0]); N Integer.parseInt(arr[0]) Integer.parseInt Integer arr[0] arr 0 int D = Integer.parseInt(arr[1]); D Integer.parseInt(arr[1]) Integer.parseInt Integer arr[1] arr 1 int a = D * 2 + 1; a D * 2 + 1 D * 2 D 2 1 int b = N / a; b N / a N a if(N % a > 0) b++; N % a > 0 N % a N a 0 b++ b System.out.println(b) System.out.println System.out System System.out b String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        // 入力受取
        BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
        String line1 = input.readLine();

        String[] arr = line1.split(" ");
        int N = Integer.parseInt(arr[0]);
        int D = Integer.parseInt(arr[1]);

        // 1人が見れる本数
        int a = D * 2 + 1;
        // N本を見るために必要な監視員
        int b = N / a;
        if(N % a > 0) b++;

        System.out.println(b);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        // 入力受取
        BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
        String line1 = input.readLine();

        String[] arr = line1.split(" ");
        int N = Integer.parseInt(arr[0]);
        int D = Integer.parseInt(arr[1]);

        // 1人が見れる本数
        int a = D * 2 + 1;
        // N本を見るために必要な監視員
        int b = N / a;
        if(N % a > 0) b++;

        System.out.println(b);
    }
} Main
import java.util.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    public static void main(String[] args) throws Exception {
        // 入力受取
        BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
        String line1 = input.readLine();

        String[] arr = line1.split(" ");
        int N = Integer.parseInt(arr[0]);
        int D = Integer.parseInt(arr[1]);

        // 1人が見れる本数
        int a = D * 2 + 1;
        // N本を見るために必要な監視員
        int b = N / a;
        if(N % a > 0) b++;

        System.out.println(b);
    }
}
