
import 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 tmpD = 2 * D + 1;

        if(N % tmpD == 0){
            System.out.println(N/tmpD);
        }else{
            System.out.println(N/tmpD + 1);
        }

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

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        int N = scanner.nextInt();
        int D = scanner.nextInt();

        int tmpD = 2 * D + 1;

        if(N % tmpD == 0){
            System.out.println(N/tmpD);
        }else{
            System.out.println(N/tmpD + 1);
        }

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

        Scanner scanner = new Scanner(System.in);

        int N = scanner.nextInt();
        int D = scanner.nextInt();

        int tmpD = 2 * D + 1;

        if(N % tmpD == 0){
            System.out.println(N/tmpD);
        }else{
            System.out.println(N/tmpD + 1);
        }

    } main {

        Scanner scanner = new Scanner(System.in);

        int N = scanner.nextInt();
        int D = scanner.nextInt();

        int tmpD = 2 * D + 1;

        if(N % tmpD == 0){
            System.out.println(N/tmpD);
        }else{
            System.out.println(N/tmpD + 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 tmpD = 2 * D + 1; tmpD 2 * D + 1 2 * D 2 D 1 if(N % tmpD == 0){
            System.out.println(N/tmpD);
        }else{
            System.out.println(N/tmpD + 1);
        } N % tmpD == 0 N % tmpD N tmpD 0 {
            System.out.println(N/tmpD);
        } System.out.println(N/tmpD) System.out.println System.out System System.out N/tmpD N tmpD {
            System.out.println(N/tmpD + 1);
        } System.out.println(N/tmpD + 1) System.out.println System.out System System.out N/tmpD + 1 N/tmpD N tmpD 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 tmpD = 2 * D + 1;

        if(N % tmpD == 0){
            System.out.println(N/tmpD);
        }else{
            System.out.println(N/tmpD + 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 tmpD = 2 * D + 1;

        if(N % tmpD == 0){
            System.out.println(N/tmpD);
        }else{
            System.out.println(N/tmpD + 1);
        }

    }
} Main

import 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 tmpD = 2 * D + 1;

        if(N % tmpD == 0){
            System.out.println(N/tmpD);
        }else{
            System.out.println(N/tmpD + 1);
        }

    }
}
