import java.util.Scanner;

public class Main {

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

		double n = Double.parseDouble(sc.next());
		double d = Double.parseDouble(sc.next());

		System.out.println((int)Math.ceil(n / (d*2+1)));
	}
} import java.util.Scanner; Scanner java.util public class Main {

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

		double n = Double.parseDouble(sc.next());
		double d = Double.parseDouble(sc.next());

		System.out.println((int)Math.ceil(n / (d*2+1)));
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		double n = Double.parseDouble(sc.next());
		double d = Double.parseDouble(sc.next());

		System.out.println((int)Math.ceil(n / (d*2+1)));
	} main {
		Scanner sc = new Scanner(System.in);

		double n = Double.parseDouble(sc.next());
		double d = Double.parseDouble(sc.next());

		System.out.println((int)Math.ceil(n / (d*2+1)));
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double n = Double.parseDouble(sc.next()); n Double.parseDouble(sc.next()) Double.parseDouble Double sc.next() sc.next sc double d = Double.parseDouble(sc.next()); d Double.parseDouble(sc.next()) Double.parseDouble Double sc.next() sc.next sc System.out.println((int)Math.ceil(n / (d*2+1))) System.out.println System.out System System.out (int)Math.ceil(n / (d*2+1)) Math.ceil Math n / (d*2+1) n (d*2+1) d*2 d 2 1 String[] args args public class Main {

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

		double n = Double.parseDouble(sc.next());
		double d = Double.parseDouble(sc.next());

		System.out.println((int)Math.ceil(n / (d*2+1)));
	}
} public class Main {

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

		double n = Double.parseDouble(sc.next());
		double d = Double.parseDouble(sc.next());

		System.out.println((int)Math.ceil(n / (d*2+1)));
	}
} Main
import java.util.Scanner;

public class Main {

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

		double n = Double.parseDouble(sc.next());
		double d = Double.parseDouble(sc.next());

		System.out.println((int)Math.ceil(n / (d*2+1)));
	}
}