import java.util.Scanner;

public class Main{

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);

		String[] tmp = scanner.nextLine().split(" ");
		int n = Integer.parseInt(tmp[0]);
		int d = Integer.parseInt(tmp[1]);

		double range = d * 2 + 1;
		double ra = n / range;
		int ans = (int)Math.ceil(ra);
		System.out.println(ans);


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

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);

		String[] tmp = scanner.nextLine().split(" ");
		int n = Integer.parseInt(tmp[0]);
		int d = Integer.parseInt(tmp[1]);

		double range = d * 2 + 1;
		double ra = n / range;
		int ans = (int)Math.ceil(ra);
		System.out.println(ans);


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

		Scanner scanner = new Scanner(System.in);

		String[] tmp = scanner.nextLine().split(" ");
		int n = Integer.parseInt(tmp[0]);
		int d = Integer.parseInt(tmp[1]);

		double range = d * 2 + 1;
		double ra = n / range;
		int ans = (int)Math.ceil(ra);
		System.out.println(ans);


	} main {

		Scanner scanner = new Scanner(System.in);

		String[] tmp = scanner.nextLine().split(" ");
		int n = Integer.parseInt(tmp[0]);
		int d = Integer.parseInt(tmp[1]);

		double range = d * 2 + 1;
		double ra = n / range;
		int ans = (int)Math.ceil(ra);
		System.out.println(ans);


	} Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) String[] tmp = scanner.nextLine().split(" "); tmp scanner.nextLine().split(" ") scanner.nextLine().split scanner.nextLine() scanner.nextLine scanner " " int n = Integer.parseInt(tmp[0]); n Integer.parseInt(tmp[0]) Integer.parseInt Integer tmp[0] tmp 0 int d = Integer.parseInt(tmp[1]); d Integer.parseInt(tmp[1]) Integer.parseInt Integer tmp[1] tmp 1 double range = d * 2 + 1; range d * 2 + 1 d * 2 d 2 1 double ra = n / range; ra n / range n range int ans = (int)Math.ceil(ra); ans (int)Math.ceil(ra) Math.ceil Math ra System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main{

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);

		String[] tmp = scanner.nextLine().split(" ");
		int n = Integer.parseInt(tmp[0]);
		int d = Integer.parseInt(tmp[1]);

		double range = d * 2 + 1;
		double ra = n / range;
		int ans = (int)Math.ceil(ra);
		System.out.println(ans);


	}
} public class Main{

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);

		String[] tmp = scanner.nextLine().split(" ");
		int n = Integer.parseInt(tmp[0]);
		int d = Integer.parseInt(tmp[1]);

		double range = d * 2 + 1;
		double ra = n / range;
		int ans = (int)Math.ceil(ra);
		System.out.println(ans);


	}
} Main
import java.util.Scanner;

public class Main{

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);

		String[] tmp = scanner.nextLine().split(" ");
		int n = Integer.parseInt(tmp[0]);
		int d = Integer.parseInt(tmp[1]);

		double range = d * 2 + 1;
		double ra = n / range;
		int ans = (int)Math.ceil(ra);
		System.out.println(ans);


	}
}
