
import java.util.Scanner;
class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int N = Integer.parseInt(sc.next());
		int D = Integer.parseInt(sc.next());

		int a = N / (2*D + 1);
		int b = N % (2*D + 1);
		if(b == 0) {
			System.out.println(a);
		} else {
			System.out.println(a+1);
		}
	}

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

		int N = Integer.parseInt(sc.next());
		int D = Integer.parseInt(sc.next());

		int a = N / (2*D + 1);
		int b = N % (2*D + 1);
		if(b == 0) {
			System.out.println(a);
		} else {
			System.out.println(a+1);
		}
	}

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

		int N = Integer.parseInt(sc.next());
		int D = Integer.parseInt(sc.next());

		int a = N / (2*D + 1);
		int b = N % (2*D + 1);
		if(b == 0) {
			System.out.println(a);
		} else {
			System.out.println(a+1);
		}
	} main {
		Scanner sc = new Scanner(System.in);

		int N = Integer.parseInt(sc.next());
		int D = Integer.parseInt(sc.next());

		int a = N / (2*D + 1);
		int b = N % (2*D + 1);
		if(b == 0) {
			System.out.println(a);
		} else {
			System.out.println(a+1);
		}
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = Integer.parseInt(sc.next()); N Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int D = Integer.parseInt(sc.next()); D Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int a = N / (2*D + 1); a N / (2*D + 1) N (2*D + 1) 2*D 2 D 1 int b = N % (2*D + 1); b N % (2*D + 1) N (2*D + 1) 2*D 2 D 1 if(b == 0) {
			System.out.println(a);
		} else {
			System.out.println(a+1);
		} b == 0 b 0 {
			System.out.println(a);
		} System.out.println(a) System.out.println System.out System System.out a {
			System.out.println(a+1);
		} System.out.println(a+1) System.out.println System.out System System.out a+1 a 1 String[] args args

import java.util.Scanner;
class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int N = Integer.parseInt(sc.next());
		int D = Integer.parseInt(sc.next());

		int a = N / (2*D + 1);
		int b = N % (2*D + 1);
		if(b == 0) {
			System.out.println(a);
		} else {
			System.out.println(a+1);
		}
	}

}
