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 answer = 0;

		while (true) {
			if (N <= (2 * D + 1) * answer) break;
			answer++;
		}

		System.out.println(answer);
	}
} 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 answer = 0;

		while (true) {
			if (N <= (2 * D + 1) * answer) break;
			answer++;
		}

		System.out.println(answer);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int answer = 0;

		while (true) {
			if (N <= (2 * D + 1) * answer) break;
			answer++;
		}

		System.out.println(answer);
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int answer = 0;

		while (true) {
			if (N <= (2 * D + 1) * answer) break;
			answer++;
		}

		System.out.println(answer);
	} 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 answer = 0; answer 0 while (true) {
			if (N <= (2 * D + 1) * answer) break;
			answer++;
		} true {
			if (N <= (2 * D + 1) * answer) break;
			answer++;
		} if (N <= (2 * D + 1) * answer) break; N <= (2 * D + 1) * answer N (2 * D + 1) * answer (2 * D + 1) 2 * D 2 D 1 answer break; answer++ answer System.out.println(answer) System.out.println System.out System System.out answer 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 answer = 0;

		while (true) {
			if (N <= (2 * D + 1) * answer) break;
			answer++;
		}

		System.out.println(answer);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		int answer = 0;

		while (true) {
			if (N <= (2 * D + 1) * answer) break;
			answer++;
		}

		System.out.println(answer);
	}
} 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 answer = 0;

		while (true) {
			if (N <= (2 * D + 1) * answer) break;
			answer++;
		}

		System.out.println(answer);
	}
}
