import java.util.Scanner;

public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int range = scan.nextInt() * 2 + 1;

		int answer = 0;
		if (n % range == 0) {
			answer = n / range;
		} else {
			answer = n /range + 1;
		}
		System.out.println(answer);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int range = scan.nextInt() * 2 + 1;

		int answer = 0;
		if (n % range == 0) {
			answer = n / range;
		} else {
			answer = n /range + 1;
		}
		System.out.println(answer);
	}
} Main public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int range = scan.nextInt() * 2 + 1;

		int answer = 0;
		if (n % range == 0) {
			answer = n / range;
		} else {
			answer = n /range + 1;
		}
		System.out.println(answer);
	} main {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int range = scan.nextInt() * 2 + 1;

		int answer = 0;
		if (n % range == 0) {
			answer = n / range;
		} else {
			answer = n /range + 1;
		}
		System.out.println(answer);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int n = scan.nextInt(); n scan.nextInt() scan.nextInt scan int range = scan.nextInt() * 2 + 1; range scan.nextInt() * 2 + 1 scan.nextInt() * 2 scan.nextInt() scan.nextInt scan 2 1 int answer = 0; answer 0 if (n % range == 0) {
			answer = n / range;
		} else {
			answer = n /range + 1;
		} n % range == 0 n % range n range 0 {
			answer = n / range;
		} answer = n / range answer n / range n range {
			answer = n /range + 1;
		} answer = n /range + 1 answer n /range + 1 n /range n range 1 System.out.println(answer) System.out.println System.out System System.out answer String[] args args public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int range = scan.nextInt() * 2 + 1;

		int answer = 0;
		if (n % range == 0) {
			answer = n / range;
		} else {
			answer = n /range + 1;
		}
		System.out.println(answer);
	}
} public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int range = scan.nextInt() * 2 + 1;

		int answer = 0;
		if (n % range == 0) {
			answer = n / range;
		} else {
			answer = n /range + 1;
		}
		System.out.println(answer);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int range = scan.nextInt() * 2 + 1;

		int answer = 0;
		if (n % range == 0) {
			answer = n / range;
		} else {
			answer = n /range + 1;
		}
		System.out.println(answer);
	}
}