import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int n, d;
		n = in.nextInt();
		d = in.nextInt();
		if (n % (2 * d + 1) == 0) {
			System.out.println(n / (2 * d + 1));
		} else {
			System.out.println(n / (2 * d + 1) + 1);
		}
		in.close();
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int n, d;
		n = in.nextInt();
		d = in.nextInt();
		if (n % (2 * d + 1) == 0) {
			System.out.println(n / (2 * d + 1));
		} else {
			System.out.println(n / (2 * d + 1) + 1);
		}
		in.close();
	}
} Main public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int n, d;
		n = in.nextInt();
		d = in.nextInt();
		if (n % (2 * d + 1) == 0) {
			System.out.println(n / (2 * d + 1));
		} else {
			System.out.println(n / (2 * d + 1) + 1);
		}
		in.close();
	} main {
		Scanner in = new Scanner(System.in);
		int n, d;
		n = in.nextInt();
		d = in.nextInt();
		if (n % (2 * d + 1) == 0) {
			System.out.println(n / (2 * d + 1));
		} else {
			System.out.println(n / (2 * d + 1) + 1);
		}
		in.close();
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) int n n d; d n = in.nextInt() n in.nextInt() in.nextInt in d = in.nextInt() d in.nextInt() in.nextInt in if (n % (2 * d + 1) == 0) {
			System.out.println(n / (2 * d + 1));
		} else {
			System.out.println(n / (2 * d + 1) + 1);
		} n % (2 * d + 1) == 0 n % (2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 0 {
			System.out.println(n / (2 * d + 1));
		} System.out.println(n / (2 * d + 1)) System.out.println System.out System System.out n / (2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 {
			System.out.println(n / (2 * d + 1) + 1);
		} System.out.println(n / (2 * d + 1) + 1) System.out.println System.out System System.out n / (2 * d + 1) + 1 n / (2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 1 in.close() in.close in String[] args args public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int n, d;
		n = in.nextInt();
		d = in.nextInt();
		if (n % (2 * d + 1) == 0) {
			System.out.println(n / (2 * d + 1));
		} else {
			System.out.println(n / (2 * d + 1) + 1);
		}
		in.close();
	}
} public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int n, d;
		n = in.nextInt();
		d = in.nextInt();
		if (n % (2 * d + 1) == 0) {
			System.out.println(n / (2 * d + 1));
		} else {
			System.out.println(n / (2 * d + 1) + 1);
		}
		in.close();
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int n, d;
		n = in.nextInt();
		d = in.nextInt();
		if (n % (2 * d + 1) == 0) {
			System.out.println(n / (2 * d + 1));
		} else {
			System.out.println(n / (2 * d + 1) + 1);
		}
		in.close();
	}
}
