
import java.util.Scanner;

public class Main {

	Scanner scan = new Scanner(System.in);
	
	void compute() {
		int n = scan.nextInt();
		int d = scan.nextInt();
		
		System.out.println(n % (d * 2 + 1) == 0 ? n / (d * 2 + 1) : n / (d * 2 + 1) + 1);
	}
	
	
	public static void main(String...arg) {
		new Main().compute();
	}
} import java.util.Scanner; Scanner java.util public class Main {

	Scanner scan = new Scanner(System.in);
	
	void compute() {
		int n = scan.nextInt();
		int d = scan.nextInt();
		
		System.out.println(n % (d * 2 + 1) == 0 ? n / (d * 2 + 1) : n / (d * 2 + 1) + 1);
	}
	
	
	public static void main(String...arg) {
		new Main().compute();
	}
} Main Scanner scan = new Scanner(System.in); scan new Scanner(System.in) void compute() {
		int n = scan.nextInt();
		int d = scan.nextInt();
		
		System.out.println(n % (d * 2 + 1) == 0 ? n / (d * 2 + 1) : n / (d * 2 + 1) + 1);
	} compute {
		int n = scan.nextInt();
		int d = scan.nextInt();
		
		System.out.println(n % (d * 2 + 1) == 0 ? n / (d * 2 + 1) : n / (d * 2 + 1) + 1);
	} int n = scan.nextInt(); n scan.nextInt() scan.nextInt scan int d = scan.nextInt(); d scan.nextInt() scan.nextInt scan System.out.println(n % (d * 2 + 1) == 0 ? n / (d * 2 + 1) : n / (d * 2 + 1) + 1) System.out.println System.out System System.out n % (d * 2 + 1) == 0 ? n / (d * 2 + 1) : n / (d * 2 + 1) + 1 n % (d * 2 + 1) == 0 n % (d * 2 + 1) n (d * 2 + 1) d * 2 d 2 1 0 n / (d * 2 + 1) n (d * 2 + 1) d * 2 d 2 1 n / (d * 2 + 1) + 1 n / (d * 2 + 1) n (d * 2 + 1) d * 2 d 2 1 1 public static void main(String...arg) {
		new Main().compute();
	} main {
		new Main().compute();
	} new Main().compute() new Main().compute new Main() String...arg arg public class Main {

	Scanner scan = new Scanner(System.in);
	
	void compute() {
		int n = scan.nextInt();
		int d = scan.nextInt();
		
		System.out.println(n % (d * 2 + 1) == 0 ? n / (d * 2 + 1) : n / (d * 2 + 1) + 1);
	}
	
	
	public static void main(String...arg) {
		new Main().compute();
	}
} public class Main {

	Scanner scan = new Scanner(System.in);
	
	void compute() {
		int n = scan.nextInt();
		int d = scan.nextInt();
		
		System.out.println(n % (d * 2 + 1) == 0 ? n / (d * 2 + 1) : n / (d * 2 + 1) + 1);
	}
	
	
	public static void main(String...arg) {
		new Main().compute();
	}
} Main

import java.util.Scanner;

public class Main {

	Scanner scan = new Scanner(System.in);
	
	void compute() {
		int n = scan.nextInt();
		int d = scan.nextInt();
		
		System.out.println(n % (d * 2 + 1) == 0 ? n / (d * 2 + 1) : n / (d * 2 + 1) + 1);
	}
	
	
	public static void main(String...arg) {
		new Main().compute();
	}
}
