import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String point = sc.nextLine();

        String[] points = point.split(" ");
        int n = Integer.parseInt(points[0]);
        int d = Integer.parseInt(points[1]);

        double d2 = d * 2.0 + 1;

        //きりあげ
        double kiriage = Math.ceil(n / d2);

        System.out.println((int)kiriage);
    }
} import java.util.*; util.* java public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String point = sc.nextLine();

        String[] points = point.split(" ");
        int n = Integer.parseInt(points[0]);
        int d = Integer.parseInt(points[1]);

        double d2 = d * 2.0 + 1;

        //きりあげ
        double kiriage = Math.ceil(n / d2);

        System.out.println((int)kiriage);
    }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String point = sc.nextLine();

        String[] points = point.split(" ");
        int n = Integer.parseInt(points[0]);
        int d = Integer.parseInt(points[1]);

        double d2 = d * 2.0 + 1;

        //きりあげ
        double kiriage = Math.ceil(n / d2);

        System.out.println((int)kiriage);
    } main {
        Scanner sc = new Scanner(System.in);
        String point = sc.nextLine();

        String[] points = point.split(" ");
        int n = Integer.parseInt(points[0]);
        int d = Integer.parseInt(points[1]);

        double d2 = d * 2.0 + 1;

        //きりあげ
        double kiriage = Math.ceil(n / d2);

        System.out.println((int)kiriage);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String point = sc.nextLine(); point sc.nextLine() sc.nextLine sc String[] points = point.split(" "); points point.split(" ") point.split point " " int n = Integer.parseInt(points[0]); n Integer.parseInt(points[0]) Integer.parseInt Integer points[0] points 0 int d = Integer.parseInt(points[1]); d Integer.parseInt(points[1]) Integer.parseInt Integer points[1] points 1 double d2 = d * 2.0 + 1; d2 d * 2.0 + 1 d * 2.0 d 2.0 1 double kiriage = Math.ceil(n / d2); kiriage Math.ceil(n / d2) Math.ceil Math n / d2 n d2 System.out.println((int)kiriage) System.out.println System.out System System.out (int)kiriage String[] args args public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String point = sc.nextLine();

        String[] points = point.split(" ");
        int n = Integer.parseInt(points[0]);
        int d = Integer.parseInt(points[1]);

        double d2 = d * 2.0 + 1;

        //きりあげ
        double kiriage = Math.ceil(n / d2);

        System.out.println((int)kiriage);
    }
} public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String point = sc.nextLine();

        String[] points = point.split(" ");
        int n = Integer.parseInt(points[0]);
        int d = Integer.parseInt(points[1]);

        double d2 = d * 2.0 + 1;

        //きりあげ
        double kiriage = Math.ceil(n / d2);

        System.out.println((int)kiriage);
    }
} Main
import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String point = sc.nextLine();

        String[] points = point.split(" ");
        int n = Integer.parseInt(points[0]);
        int d = Integer.parseInt(points[1]);

        double d2 = d * 2.0 + 1;

        //きりあげ
        double kiriage = Math.ceil(n / d2);

        System.out.println((int)kiriage);
    }
}