import java.util.Scanner;

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

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int D = sc.nextInt();
		int n = 0;
		int count = 0;

		for (int i = 0; i < N; i++) {
			n += 2 * D + 1;
			count++;

			if (n >= N) {
				System.out.print(count);
				break;
			}
		}
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int D = sc.nextInt();
		int n = 0;
		int count = 0;

		for (int i = 0; i < N; i++) {
			n += 2 * D + 1;
			count++;

			if (n >= N) {
				System.out.print(count);
				break;
			}
		}
	}
} Main public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int D = sc.nextInt();
		int n = 0;
		int count = 0;

		for (int i = 0; i < N; i++) {
			n += 2 * D + 1;
			count++;

			if (n >= N) {
				System.out.print(count);
				break;
			}
		}
	} main {

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int D = sc.nextInt();
		int n = 0;
		int count = 0;

		for (int i = 0; i < N; i++) {
			n += 2 * D + 1;
			count++;

			if (n >= N) {
				System.out.print(count);
				break;
			}
		}
	} 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 n = 0; n 0 int count = 0; count 0 for (int i = 0; i < N; i++) {
			n += 2 * D + 1;
			count++;

			if (n >= N) {
				System.out.print(count);
				break;
			}
		} int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
			n += 2 * D + 1;
			count++;

			if (n >= N) {
				System.out.print(count);
				break;
			}
		} {
			n += 2 * D + 1;
			count++;

			if (n >= N) {
				System.out.print(count);
				break;
			}
		} n += 2 * D + 1 n 2 * D + 1 2 * D 2 D 1 count++ count if (n >= N) {
				System.out.print(count);
				break;
			} n >= N n N {
				System.out.print(count);
				break;
			} System.out.print(count) System.out.print System.out System System.out count break; String[] args args public class Main {
	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int D = sc.nextInt();
		int n = 0;
		int count = 0;

		for (int i = 0; i < N; i++) {
			n += 2 * D + 1;
			count++;

			if (n >= N) {
				System.out.print(count);
				break;
			}
		}
	}
} public class Main {
	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int D = sc.nextInt();
		int n = 0;
		int count = 0;

		for (int i = 0; i < N; i++) {
			n += 2 * D + 1;
			count++;

			if (n >= N) {
				System.out.print(count);
				break;
			}
		}
	}
} Main
import java.util.Scanner;

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

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int D = sc.nextInt();
		int n = 0;
		int count = 0;

		for (int i = 0; i < N; i++) {
			n += 2 * D + 1;
			count++;

			if (n >= N) {
				System.out.print(count);
				break;
			}
		}
	}
}