import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

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

	void run() {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int M = 2 * D + 1;
		System.out.println((N + M - 1) / M);
	}

	void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}
} import java.util.ArrayList; ArrayList java.util import java.util.Arrays; Arrays java.util import java.util.Scanner; Scanner java.util class Main {
	public static void main(String[] args) {
		new Main().run();
	}

	void run() {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int M = 2 * D + 1;
		System.out.println((N + M - 1) / M);
	}

	void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}
} Main public static void main(String[] args) {
		new Main().run();
	} main {
		new Main().run();
	} new Main().run() new Main().run new Main() String[] args args void run() {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int M = 2 * D + 1;
		System.out.println((N + M - 1) / M);
	} run {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int M = 2 * D + 1;
		System.out.println((N + M - 1) / M);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int D = sc.nextInt(); D sc.nextInt() sc.nextInt sc int M = 2 * D + 1; M 2 * D + 1 2 * D 2 D 1 System.out.println((N + M - 1) / M) System.out.println System.out System System.out (N + M - 1) / M (N + M - 1) N + M N M 1 M void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	} tr {
		System.out.println(Arrays.deepToString(objects));
	} System.out.println(Arrays.deepToString(objects)) System.out.println System.out System System.out Arrays.deepToString(objects) Arrays.deepToString Arrays objects Object... objects objects
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

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

	void run() {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int M = 2 * D + 1;
		System.out.println((N + M - 1) / M);
	}

	void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}
}