import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int N = Integer.parseInt(sc.next());
		int D = Integer.parseInt(sc.next());

		int treePerP = 2 * D + 1;

		int ans = N / treePerP;
		if (N % treePerP > 0) {
			ans += 1;
		}

		System.out.println(ans);

	}

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

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int N = Integer.parseInt(sc.next());
		int D = Integer.parseInt(sc.next());

		int treePerP = 2 * D + 1;

		int ans = N / treePerP;
		if (N % treePerP > 0) {
			ans += 1;
		}

		System.out.println(ans);

	}

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

		Scanner sc = new Scanner(System.in);

		int N = Integer.parseInt(sc.next());
		int D = Integer.parseInt(sc.next());

		int treePerP = 2 * D + 1;

		int ans = N / treePerP;
		if (N % treePerP > 0) {
			ans += 1;
		}

		System.out.println(ans);

	} main {

		Scanner sc = new Scanner(System.in);

		int N = Integer.parseInt(sc.next());
		int D = Integer.parseInt(sc.next());

		int treePerP = 2 * D + 1;

		int ans = N / treePerP;
		if (N % treePerP > 0) {
			ans += 1;
		}

		System.out.println(ans);

	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = Integer.parseInt(sc.next()); N Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int D = Integer.parseInt(sc.next()); D Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int treePerP = 2 * D + 1; treePerP 2 * D + 1 2 * D 2 D 1 int ans = N / treePerP; ans N / treePerP N treePerP if (N % treePerP > 0) {
			ans += 1;
		} N % treePerP > 0 N % treePerP N treePerP 0 {
			ans += 1;
		} ans += 1 ans 1 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 sc = new Scanner(System.in);

		int N = Integer.parseInt(sc.next());
		int D = Integer.parseInt(sc.next());

		int treePerP = 2 * D + 1;

		int ans = N / treePerP;
		if (N % treePerP > 0) {
			ans += 1;
		}

		System.out.println(ans);

	}

} public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int N = Integer.parseInt(sc.next());
		int D = Integer.parseInt(sc.next());

		int treePerP = 2 * D + 1;

		int ans = N / treePerP;
		if (N % treePerP > 0) {
			ans += 1;
		}

		System.out.println(ans);

	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int N = Integer.parseInt(sc.next());
		int D = Integer.parseInt(sc.next());

		int treePerP = 2 * D + 1;

		int ans = N / treePerP;
		if (N % treePerP > 0) {
			ans += 1;
		}

		System.out.println(ans);

	}

}
