import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		final Scanner sc = new Scanner(System.in);
		final int N = sc.nextInt();
		final int D = sc.nextInt();
		
		final int div = N / (2 * D + 1);
		final int mod = N % (2 * D + 1);
		
		if (mod == 0) {
			System.out.println(div);
		} else {
			System.out.println(div + 1);
		}
	}

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

	public static void main(String[] args) {
		final Scanner sc = new Scanner(System.in);
		final int N = sc.nextInt();
		final int D = sc.nextInt();
		
		final int div = N / (2 * D + 1);
		final int mod = N % (2 * D + 1);
		
		if (mod == 0) {
			System.out.println(div);
		} else {
			System.out.println(div + 1);
		}
	}

} Main public static void main(String[] args) {
		final Scanner sc = new Scanner(System.in);
		final int N = sc.nextInt();
		final int D = sc.nextInt();
		
		final int div = N / (2 * D + 1);
		final int mod = N % (2 * D + 1);
		
		if (mod == 0) {
			System.out.println(div);
		} else {
			System.out.println(div + 1);
		}
	} main {
		final Scanner sc = new Scanner(System.in);
		final int N = sc.nextInt();
		final int D = sc.nextInt();
		
		final int div = N / (2 * D + 1);
		final int mod = N % (2 * D + 1);
		
		if (mod == 0) {
			System.out.println(div);
		} else {
			System.out.println(div + 1);
		}
	} final Scanner sc = new Scanner(System.in); sc new Scanner(System.in) final int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc final int D = sc.nextInt(); D sc.nextInt() sc.nextInt sc final int div = N / (2 * D + 1); div N / (2 * D + 1) N (2 * D + 1) 2 * D 2 D 1 final int mod = N % (2 * D + 1); mod N % (2 * D + 1) N (2 * D + 1) 2 * D 2 D 1 if (mod == 0) {
			System.out.println(div);
		} else {
			System.out.println(div + 1);
		} mod == 0 mod 0 {
			System.out.println(div);
		} System.out.println(div) System.out.println System.out System System.out div {
			System.out.println(div + 1);
		} System.out.println(div + 1) System.out.println System.out System System.out div + 1 div 1 String[] args args public class Main {

	public static void main(String[] args) {
		final Scanner sc = new Scanner(System.in);
		final int N = sc.nextInt();
		final int D = sc.nextInt();
		
		final int div = N / (2 * D + 1);
		final int mod = N % (2 * D + 1);
		
		if (mod == 0) {
			System.out.println(div);
		} else {
			System.out.println(div + 1);
		}
	}

} public class Main {

	public static void main(String[] args) {
		final Scanner sc = new Scanner(System.in);
		final int N = sc.nextInt();
		final int D = sc.nextInt();
		
		final int div = N / (2 * D + 1);
		final int mod = N % (2 * D + 1);
		
		if (mod == 0) {
			System.out.println(div);
		} else {
			System.out.println(div + 1);
		}
	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		final Scanner sc = new Scanner(System.in);
		final int N = sc.nextInt();
		final int D = sc.nextInt();
		
		final int div = N / (2 * D + 1);
		final int mod = N % (2 * D + 1);
		
		if (mod == 0) {
			System.out.println(div);
		} else {
			System.out.println(div + 1);
		}
	}

}