import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int d = scan.nextInt();

		int dd = n / (2 * d + 1);
		if(n % (2 * d + 1) != 0)
			dd++;

		System.out.println(dd);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int d = scan.nextInt();

		int dd = n / (2 * d + 1);
		if(n % (2 * d + 1) != 0)
			dd++;

		System.out.println(dd);
	}
} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int d = scan.nextInt();

		int dd = n / (2 * d + 1);
		if(n % (2 * d + 1) != 0)
			dd++;

		System.out.println(dd);
	} main {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int d = scan.nextInt();

		int dd = n / (2 * d + 1);
		if(n % (2 * d + 1) != 0)
			dd++;

		System.out.println(dd);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int n = scan.nextInt(); n scan.nextInt() scan.nextInt scan int d = scan.nextInt(); d scan.nextInt() scan.nextInt scan int dd = n / (2 * d + 1); dd n / (2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 if(n % (2 * d + 1) != 0)
			dd++; n % (2 * d + 1) != 0 n % (2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 0 dd++ dd System.out.println(dd) System.out.println System.out System System.out dd String[] args args public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int d = scan.nextInt();

		int dd = n / (2 * d + 1);
		if(n % (2 * d + 1) != 0)
			dd++;

		System.out.println(dd);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int d = scan.nextInt();

		int dd = n / (2 * d + 1);
		if(n % (2 * d + 1) != 0)
			dd++;

		System.out.println(dd);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int d = scan.nextInt();

		int dd = n / (2 * d + 1);
		if(n % (2 * d + 1) != 0)
			dd++;

		System.out.println(dd);
	}
}
