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 a = n / ((2*d) + 1);
		int b = n %((2*d) + 1);
		if (b > 0) a++;

		System.out.println(a);

		sc.close();
	}
} 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 a = n / ((2*d) + 1);
		int b = n %((2*d) + 1);
		if (b > 0) a++;

		System.out.println(a);

		sc.close();
	}
} Main public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d  =sc.nextInt();

		int a = n / ((2*d) + 1);
		int b = n %((2*d) + 1);
		if (b > 0) a++;

		System.out.println(a);

		sc.close();
	} main {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d  =sc.nextInt();

		int a = n / ((2*d) + 1);
		int b = n %((2*d) + 1);
		if (b > 0) a++;

		System.out.println(a);

		sc.close();
	} 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 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) a++; b > 0 b 0 a++ a System.out.println(a) System.out.println System.out System System.out a sc.close() sc.close sc 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 a = n / ((2*d) + 1);
		int b = n %((2*d) + 1);
		if (b > 0) a++;

		System.out.println(a);

		sc.close();
	}
} public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d  =sc.nextInt();

		int a = n / ((2*d) + 1);
		int b = n %((2*d) + 1);
		if (b > 0) a++;

		System.out.println(a);

		sc.close();
	}
} 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 a = n / ((2*d) + 1);
		int b = n %((2*d) + 1);
		if (b > 0) a++;

		System.out.println(a);

		sc.close();
	}
}
