import java.util.Scanner;

public class Main {
	Scanner sc = new Scanner(System.in);
	
	void a() {
		int r = sc.nextInt();
		System.out.println(3 * r  * r);
	}
	
	void b() {
		int n = sc.nextInt(),d = sc.nextInt();
		int range = d * 2 + 1;
		if(n % range == 0) System.out.println(n / range);
		else System.out.println(n / range + 1);
	}

	public static void main(String[] args) {
		new Main().b();
	}

} import java.util.Scanner; Scanner java.util public class Main {
	Scanner sc = new Scanner(System.in);
	
	void a() {
		int r = sc.nextInt();
		System.out.println(3 * r  * r);
	}
	
	void b() {
		int n = sc.nextInt(),d = sc.nextInt();
		int range = d * 2 + 1;
		if(n % range == 0) System.out.println(n / range);
		else System.out.println(n / range + 1);
	}

	public static void main(String[] args) {
		new Main().b();
	}

} Main Scanner sc = new Scanner(System.in); sc new Scanner(System.in) void a() {
		int r = sc.nextInt();
		System.out.println(3 * r  * r);
	} a {
		int r = sc.nextInt();
		System.out.println(3 * r  * r);
	} int r = sc.nextInt(); r sc.nextInt() sc.nextInt sc System.out.println(3 * r  * r) System.out.println System.out System System.out 3 * r  * r 3 * r  * r 3 r r void b() {
		int n = sc.nextInt(),d = sc.nextInt();
		int range = d * 2 + 1;
		if(n % range == 0) System.out.println(n / range);
		else System.out.println(n / range + 1);
	} b {
		int n = sc.nextInt(),d = sc.nextInt();
		int range = d * 2 + 1;
		if(n % range == 0) System.out.println(n / range);
		else System.out.println(n / range + 1);
	} int n = sc.nextInt() n sc.nextInt() sc.nextInt sc d = sc.nextInt(); d sc.nextInt() sc.nextInt sc int range = d * 2 + 1; range d * 2 + 1 d * 2 d 2 1 if(n % range == 0) System.out.println(n / range);
		else System.out.println(n / range + 1); n % range == 0 n % range n range 0 System.out.println(n / range) System.out.println System.out System System.out n / range n range System.out.println(n / range + 1) System.out.println System.out System System.out n / range + 1 n / range n range 1 public static void main(String[] args) {
		new Main().b();
	} main {
		new Main().b();
	} new Main().b() new Main().b new Main() String[] args args public class Main {
	Scanner sc = new Scanner(System.in);
	
	void a() {
		int r = sc.nextInt();
		System.out.println(3 * r  * r);
	}
	
	void b() {
		int n = sc.nextInt(),d = sc.nextInt();
		int range = d * 2 + 1;
		if(n % range == 0) System.out.println(n / range);
		else System.out.println(n / range + 1);
	}

	public static void main(String[] args) {
		new Main().b();
	}

} public class Main {
	Scanner sc = new Scanner(System.in);
	
	void a() {
		int r = sc.nextInt();
		System.out.println(3 * r  * r);
	}
	
	void b() {
		int n = sc.nextInt(),d = sc.nextInt();
		int range = d * 2 + 1;
		if(n % range == 0) System.out.println(n / range);
		else System.out.println(n / range + 1);
	}

	public static void main(String[] args) {
		new Main().b();
	}

} Main
import java.util.Scanner;

public class Main {
	Scanner sc = new Scanner(System.in);
	
	void a() {
		int r = sc.nextInt();
		System.out.println(3 * r  * r);
	}
	
	void b() {
		int n = sc.nextInt(),d = sc.nextInt();
		int range = d * 2 + 1;
		if(n % range == 0) System.out.println(n / range);
		else System.out.println(n / range + 1);
	}

	public static void main(String[] args) {
		new Main().b();
	}

}
