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 range = 2*D+1;
        int result;
        if (N%range == 0){
            result = N / range;
        }else{
            result = N / range + 1;
        }

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

        System.out.println(result);
    }
} Main public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int D = scanner.nextInt();

        int range = 2*D+1;
        int result;
        if (N%range == 0){
            result = N / range;
        }else{
            result = N / range + 1;
        }

        System.out.println(result);
    } main {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int D = scanner.nextInt();

        int range = 2*D+1;
        int result;
        if (N%range == 0){
            result = N / range;
        }else{
            result = N / range + 1;
        }

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

        System.out.println(result);
    }
} public class Main {
    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int D = scanner.nextInt();

        int range = 2*D+1;
        int result;
        if (N%range == 0){
            result = N / range;
        }else{
            result = N / range + 1;
        }

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

        System.out.println(result);
    }
}
