import java.io.InputStream;
import java.io.PrintStream;
import java.util.Scanner;

public class Main {
	InputStream in = System.in;
	PrintStream out = System.out;

	public void _main(String[] args) {
		Scanner sc = new Scanner(in);

		int N = sc.nextInt();
		int D = sc.nextInt();

		sc.close();

		int d = 2 * D + 1;

		out.println((N + d - 1) / d);

	}

	public static void main(String[] args) {
		new Main()._main(args);
	}
} import java.io.InputStream; InputStream java.io import java.io.PrintStream; PrintStream java.io import java.util.Scanner; Scanner java.util public class Main {
	InputStream in = System.in;
	PrintStream out = System.out;

	public void _main(String[] args) {
		Scanner sc = new Scanner(in);

		int N = sc.nextInt();
		int D = sc.nextInt();

		sc.close();

		int d = 2 * D + 1;

		out.println((N + d - 1) / d);

	}

	public static void main(String[] args) {
		new Main()._main(args);
	}
} Main InputStream in = System.in; in System.in System System.in PrintStream out = System.out; out System.out System System.out public void _main(String[] args) {
		Scanner sc = new Scanner(in);

		int N = sc.nextInt();
		int D = sc.nextInt();

		sc.close();

		int d = 2 * D + 1;

		out.println((N + d - 1) / d);

	} _main {
		Scanner sc = new Scanner(in);

		int N = sc.nextInt();
		int D = sc.nextInt();

		sc.close();

		int d = 2 * D + 1;

		out.println((N + d - 1) / d);

	} Scanner sc = new Scanner(in); sc new Scanner(in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int D = sc.nextInt(); D sc.nextInt() sc.nextInt sc sc.close() sc.close sc int d = 2 * D + 1; d 2 * D + 1 2 * D 2 D 1 out.println((N + d - 1) / d) out.println out (N + d - 1) / d (N + d - 1) N + d N d 1 d String[] args args public static void main(String[] args) {
		new Main()._main(args);
	} main {
		new Main()._main(args);
	} new Main()._main(args) new Main()._main new Main() args String[] args args public class Main {
	InputStream in = System.in;
	PrintStream out = System.out;

	public void _main(String[] args) {
		Scanner sc = new Scanner(in);

		int N = sc.nextInt();
		int D = sc.nextInt();

		sc.close();

		int d = 2 * D + 1;

		out.println((N + d - 1) / d);

	}

	public static void main(String[] args) {
		new Main()._main(args);
	}
} public class Main {
	InputStream in = System.in;
	PrintStream out = System.out;

	public void _main(String[] args) {
		Scanner sc = new Scanner(in);

		int N = sc.nextInt();
		int D = sc.nextInt();

		sc.close();

		int d = 2 * D + 1;

		out.println((N + d - 1) / d);

	}

	public static void main(String[] args) {
		new Main()._main(args);
	}
} Main
import java.io.InputStream;
import java.io.PrintStream;
import java.util.Scanner;

public class Main {
	InputStream in = System.in;
	PrintStream out = System.out;

	public void _main(String[] args) {
		Scanner sc = new Scanner(in);

		int N = sc.nextInt();
		int D = sc.nextInt();

		sc.close();

		int d = 2 * D + 1;

		out.println((N + d - 1) / d);

	}

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