import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		long n = in.nextInt();
		long d = in.nextInt();
		long ans;

		ans = (long) Math.ceil((double)n / (d*2+1));



		System.out.println(ans);
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		long n = in.nextInt();
		long d = in.nextInt();
		long ans;

		ans = (long) Math.ceil((double)n / (d*2+1));



		System.out.println(ans);
	}
} Main public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		long n = in.nextInt();
		long d = in.nextInt();
		long ans;

		ans = (long) Math.ceil((double)n / (d*2+1));



		System.out.println(ans);
	} main {
		Scanner in = new Scanner(System.in);
		long n = in.nextInt();
		long d = in.nextInt();
		long ans;

		ans = (long) Math.ceil((double)n / (d*2+1));



		System.out.println(ans);
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) long n = in.nextInt(); n in.nextInt() in.nextInt in long d = in.nextInt(); d in.nextInt() in.nextInt in long ans; ans ans = (long) Math.ceil((double)n / (d*2+1)) ans (long) Math.ceil((double)n / (d*2+1)) Math.ceil Math (double)n / (d*2+1) (double)n (d*2+1) d*2 d 2 1 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		long n = in.nextInt();
		long d = in.nextInt();
		long ans;

		ans = (long) Math.ceil((double)n / (d*2+1));



		System.out.println(ans);
	}
} public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		long n = in.nextInt();
		long d = in.nextInt();
		long ans;

		ans = (long) Math.ceil((double)n / (d*2+1));



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

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		long n = in.nextInt();
		long d = in.nextInt();
		long ans;

		ans = (long) Math.ceil((double)n / (d*2+1));



		System.out.println(ans);
	}
}
