
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 ans;


		if(N/2 <= D) {
			ans = 1;
		}else if(N%(2*D+1) == 0){
			ans = N/(2*D+1);
		}else {
			ans = N/(2*D+1) + 1;
		}

		System.out.println(ans);
	}

} 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 ans;


		if(N/2 <= D) {
			ans = 1;
		}else if(N%(2*D+1) == 0){
			ans = N/(2*D+1);
		}else {
			ans = N/(2*D+1) + 1;
		}

		System.out.println(ans);
	}

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

		Scanner sc = new Scanner(System.in);


		int N = sc.nextInt();
		int D = sc.nextInt();
		int ans;


		if(N/2 <= D) {
			ans = 1;
		}else if(N%(2*D+1) == 0){
			ans = N/(2*D+1);
		}else {
			ans = N/(2*D+1) + 1;
		}

		System.out.println(ans);
	} main {

		Scanner sc = new Scanner(System.in);


		int N = sc.nextInt();
		int D = sc.nextInt();
		int ans;


		if(N/2 <= D) {
			ans = 1;
		}else if(N%(2*D+1) == 0){
			ans = N/(2*D+1);
		}else {
			ans = N/(2*D+1) + 1;
		}

		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 int D = sc.nextInt(); D sc.nextInt() sc.nextInt sc int ans; ans if(N/2 <= D) {
			ans = 1;
		}else if(N%(2*D+1) == 0){
			ans = N/(2*D+1);
		}else {
			ans = N/(2*D+1) + 1;
		} N/2 <= D N/2 N 2 D {
			ans = 1;
		} ans = 1 ans 1 if(N%(2*D+1) == 0){
			ans = N/(2*D+1);
		}else {
			ans = N/(2*D+1) + 1;
		} N%(2*D+1) == 0 N%(2*D+1) N (2*D+1) 2*D 2 D 1 0 {
			ans = N/(2*D+1);
		} ans = N/(2*D+1) ans N/(2*D+1) N (2*D+1) 2*D 2 D 1 {
			ans = N/(2*D+1) + 1;
		} ans = N/(2*D+1) + 1 ans N/(2*D+1) + 1 N/(2*D+1) N (2*D+1) 2*D 2 D 1 1 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();
		int D = sc.nextInt();
		int ans;


		if(N/2 <= D) {
			ans = 1;
		}else if(N%(2*D+1) == 0){
			ans = N/(2*D+1);
		}else {
			ans = N/(2*D+1) + 1;
		}

		System.out.println(ans);
	}

} public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);


		int N = sc.nextInt();
		int D = sc.nextInt();
		int ans;


		if(N/2 <= D) {
			ans = 1;
		}else if(N%(2*D+1) == 0){
			ans = N/(2*D+1);
		}else {
			ans = N/(2*D+1) + 1;
		}

		System.out.println(ans);
	}

} 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 ans;


		if(N/2 <= D) {
			ans = 1;
		}else if(N%(2*D+1) == 0){
			ans = N/(2*D+1);
		}else {
			ans = N/(2*D+1) + 1;
		}

		System.out.println(ans);
	}

}