
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		String line = sc.nextLine();
		String[] lines = line.split(" ");

		int N = Integer.parseInt(lines[0]);
		int D = Integer.parseInt(lines[1]);

		int num = 2*D + 1;
		int ans = N / num;
		if(N % num == 0) {
			System.out.println(ans);
		}else {
			System.out.println(ans + 1);
		}
	}

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

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		String line = sc.nextLine();
		String[] lines = line.split(" ");

		int N = Integer.parseInt(lines[0]);
		int D = Integer.parseInt(lines[1]);

		int num = 2*D + 1;
		int ans = N / num;
		if(N % num == 0) {
			System.out.println(ans);
		}else {
			System.out.println(ans + 1);
		}
	}

} Main public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		String line = sc.nextLine();
		String[] lines = line.split(" ");

		int N = Integer.parseInt(lines[0]);
		int D = Integer.parseInt(lines[1]);

		int num = 2*D + 1;
		int ans = N / num;
		if(N % num == 0) {
			System.out.println(ans);
		}else {
			System.out.println(ans + 1);
		}
	} main {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		String line = sc.nextLine();
		String[] lines = line.split(" ");

		int N = Integer.parseInt(lines[0]);
		int D = Integer.parseInt(lines[1]);

		int num = 2*D + 1;
		int ans = N / num;
		if(N % num == 0) {
			System.out.println(ans);
		}else {
			System.out.println(ans + 1);
		}
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String line = sc.nextLine(); line sc.nextLine() sc.nextLine sc String[] lines = line.split(" "); lines line.split(" ") line.split line " " int N = Integer.parseInt(lines[0]); N Integer.parseInt(lines[0]) Integer.parseInt Integer lines[0] lines 0 int D = Integer.parseInt(lines[1]); D Integer.parseInt(lines[1]) Integer.parseInt Integer lines[1] lines 1 int num = 2*D + 1; num 2*D + 1 2*D 2 D 1 int ans = N / num; ans N / num N num if(N % num == 0) {
			System.out.println(ans);
		}else {
			System.out.println(ans + 1);
		} N % num == 0 N % num N num 0 {
			System.out.println(ans);
		} System.out.println(ans) System.out.println System.out System System.out ans {
			System.out.println(ans + 1);
		} System.out.println(ans + 1) System.out.println System.out System System.out ans + 1 ans 1 String[] args args public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		String line = sc.nextLine();
		String[] lines = line.split(" ");

		int N = Integer.parseInt(lines[0]);
		int D = Integer.parseInt(lines[1]);

		int num = 2*D + 1;
		int ans = N / num;
		if(N % num == 0) {
			System.out.println(ans);
		}else {
			System.out.println(ans + 1);
		}
	}

} public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		String line = sc.nextLine();
		String[] lines = line.split(" ");

		int N = Integer.parseInt(lines[0]);
		int D = Integer.parseInt(lines[1]);

		int num = 2*D + 1;
		int ans = N / num;
		if(N % num == 0) {
			System.out.println(ans);
		}else {
			System.out.println(ans + 1);
		}
	}

} Main

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		String line = sc.nextLine();
		String[] lines = line.split(" ");

		int N = Integer.parseInt(lines[0]);
		int D = Integer.parseInt(lines[1]);

		int num = 2*D + 1;
		int ans = N / num;
		if(N % num == 0) {
			System.out.println(ans);
		}else {
			System.out.println(ans + 1);
		}
	}

}
