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

		System.out.println(a);
	}

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

		System.out.println(a);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		sc.close();
		int a = 0;
		if(n % (2*d + 1)==0) {
			a = n / (2*d + 1);
		}else {
			a = n / (2*d + 1) +1;
		}

		System.out.println(a);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		sc.close();
		int a = 0;
		if(n % (2*d + 1)==0) {
			a = n / (2*d + 1);
		}else {
			a = n / (2*d + 1) +1;
		}

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

		System.out.println(a);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		sc.close();
		int a = 0;
		if(n % (2*d + 1)==0) {
			a = n / (2*d + 1);
		}else {
			a = n / (2*d + 1) +1;
		}

		System.out.println(a);
	}

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

		System.out.println(a);
	}

}