import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

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

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

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

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

} public class Main {

	public static void main(String[] args) {

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

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

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

}
