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 cnt = 1;
		while (cnt * (2 * d + 1) < n) {
			cnt++;
		}
		System.out.println(cnt);
	}
} 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 cnt = 1;
		while (cnt * (2 * d + 1) < n) {
			cnt++;
		}
		System.out.println(cnt);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int cnt = 1;
		while (cnt * (2 * d + 1) < n) {
			cnt++;
		}
		System.out.println(cnt);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int cnt = 1;
		while (cnt * (2 * d + 1) < n) {
			cnt++;
		}
		System.out.println(cnt);
	} 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 cnt = 1; cnt 1 while (cnt * (2 * d + 1) < n) {
			cnt++;
		} cnt * (2 * d + 1) < n cnt * (2 * d + 1) cnt (2 * d + 1) 2 * d 2 d 1 n {
			cnt++;
		} cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt 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 cnt = 1;
		while (cnt * (2 * d + 1) < n) {
			cnt++;
		}
		System.out.println(cnt);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int cnt = 1;
		while (cnt * (2 * d + 1) < n) {
			cnt++;
		}
		System.out.println(cnt);
	}
} 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 cnt = 1;
		while (cnt * (2 * d + 1) < n) {
			cnt++;
		}
		System.out.println(cnt);
	}
}
