import java.util.Scanner;


public class Main {
	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int shou = N / ( 2 * D + 1);
		int amari = N % ( 2 * D + 1);

		if (amari != 0) {
			shou++;
		}

		System.out.println(shou);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int shou = N / ( 2 * D + 1);
		int amari = N % ( 2 * D + 1);

		if (amari != 0) {
			shou++;
		}

		System.out.println(shou);
	}
} Main public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int shou = N / ( 2 * D + 1);
		int amari = N % ( 2 * D + 1);

		if (amari != 0) {
			shou++;
		}

		System.out.println(shou);
	} main {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int shou = N / ( 2 * D + 1);
		int amari = N % ( 2 * D + 1);

		if (amari != 0) {
			shou++;
		}

		System.out.println(shou);
	} Scanner scn = new Scanner(System.in); scn new Scanner(System.in) int N = scn.nextInt(); N scn.nextInt() scn.nextInt scn int D = scn.nextInt(); D scn.nextInt() scn.nextInt scn int shou = N / ( 2 * D + 1); shou N / ( 2 * D + 1) N ( 2 * D + 1) 2 * D 2 D 1 int amari = N % ( 2 * D + 1); amari N % ( 2 * D + 1) N ( 2 * D + 1) 2 * D 2 D 1 if (amari != 0) {
			shou++;
		} amari != 0 amari 0 {
			shou++;
		} shou++ shou System.out.println(shou) System.out.println System.out System System.out shou String[] args args public class Main {
	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int shou = N / ( 2 * D + 1);
		int amari = N % ( 2 * D + 1);

		if (amari != 0) {
			shou++;
		}

		System.out.println(shou);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int shou = N / ( 2 * D + 1);
		int amari = N % ( 2 * D + 1);

		if (amari != 0) {
			shou++;
		}

		System.out.println(shou);
	}
} Main
import java.util.Scanner;


public class Main {
	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int shou = N / ( 2 * D + 1);
		int amari = N % ( 2 * D + 1);

		if (amari != 0) {
			shou++;
		}

		System.out.println(shou);
	}
}
