import java.util.Scanner;

public class Main{

	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int DD = 2 * D + 1;
		System.out.println((N%DD == 0)?N/DD:N/DD+1);
	}

} import java.util.Scanner; Scanner java.util public class Main{

	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int DD = 2 * D + 1;
		System.out.println((N%DD == 0)?N/DD:N/DD+1);
	}

} Main public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int DD = 2 * D + 1;
		System.out.println((N%DD == 0)?N/DD:N/DD+1);
	} main {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int DD = 2 * D + 1;
		System.out.println((N%DD == 0)?N/DD:N/DD+1);
	} Scanner scn = new Scanner(System.in); scn new Scanner(System.in) int N = scn.nextInt(); N scn.nextInt() scn.nextInt scn int D = scn.nextInt(); D scn.nextInt() scn.nextInt scn int DD = 2 * D + 1; DD 2 * D + 1 2 * D 2 D 1 System.out.println((N%DD == 0)?N/DD:N/DD+1) System.out.println System.out System System.out (N%DD == 0)?N/DD:N/DD+1 (N%DD == 0) N%DD N DD 0 N/DD N DD N/DD+1 N/DD N DD 1 String[] args args public class Main{

	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int DD = 2 * D + 1;
		System.out.println((N%DD == 0)?N/DD:N/DD+1);
	}

} public class Main{

	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int DD = 2 * D + 1;
		System.out.println((N%DD == 0)?N/DD:N/DD+1);
	}

} Main
import java.util.Scanner;

public class Main{

	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int N = scn.nextInt();
		int D = scn.nextInt();
		int DD = 2 * D + 1;
		System.out.println((N%DD == 0)?N/DD:N/DD+1);
	}

}