import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int d = Integer.parseInt(sc.next());
		int ans = 0;
		for (int i = n; i >= 1; i--) {
			i = i - 2 * d;
			ans++;
		}
		System.out.println(ans);
		sc.close();
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int d = Integer.parseInt(sc.next());
		int ans = 0;
		for (int i = n; i >= 1; i--) {
			i = i - 2 * d;
			ans++;
		}
		System.out.println(ans);
		sc.close();
	}
} Main public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int d = Integer.parseInt(sc.next());
		int ans = 0;
		for (int i = n; i >= 1; i--) {
			i = i - 2 * d;
			ans++;
		}
		System.out.println(ans);
		sc.close();
	} main {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int d = Integer.parseInt(sc.next());
		int ans = 0;
		for (int i = n; i >= 1; i--) {
			i = i - 2 * d;
			ans++;
		}
		System.out.println(ans);
		sc.close();
	} 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 ans = 0; ans 0 for (int i = n; i >= 1; i--) {
			i = i - 2 * d;
			ans++;
		} int i = n; int i = n; i n i >= 1 i 1 i-- i-- i {
			i = i - 2 * d;
			ans++;
		} {
			i = i - 2 * d;
			ans++;
		} i = i - 2 * d i i - 2 * d i 2 * d 2 d ans++ ans System.out.println(ans) System.out.println System.out System System.out ans sc.close() sc.close sc String[] args args public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int d = Integer.parseInt(sc.next());
		int ans = 0;
		for (int i = n; i >= 1; i--) {
			i = i - 2 * d;
			ans++;
		}
		System.out.println(ans);
		sc.close();
	}
} public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int d = Integer.parseInt(sc.next());
		int ans = 0;
		for (int i = n; i >= 1; i--) {
			i = i - 2 * d;
			ans++;
		}
		System.out.println(ans);
		sc.close();
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int d = Integer.parseInt(sc.next());
		int ans = 0;
		for (int i = n; i >= 1; i--) {
			i = i - 2 * d;
			ans++;
		}
		System.out.println(ans);
		sc.close();
	}
}