import java.util.*;

public class Main {

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

		System.out.println(ans);
	}
} import java.util.*; util.* java public class Main {

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

		System.out.println(ans);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt(), d = sc.nextInt();
		sc.close();
		int tmp = 2 * d + 1;
		int r = n % tmp;
		int ans = n /tmp;
		if(r != 0)
			ans++;

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

		System.out.println(ans);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt() n sc.nextInt() sc.nextInt sc d = sc.nextInt(); d sc.nextInt() sc.nextInt sc sc.close() sc.close sc int tmp = 2 * d + 1; tmp 2 * d + 1 2 * d 2 d 1 int r = n % tmp; r n % tmp n tmp int ans = n /tmp; ans n /tmp n tmp if(r != 0)
			ans++; r != 0 r 0 ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {

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

		System.out.println(ans);
	}
} public class Main {

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

		System.out.println(ans);
	}
} Main
import java.util.*;

public class Main {

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

		System.out.println(ans);
	}
}
