import java.util.*;
import java.io.*;

public class Main {
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt(), d = sc.nextInt();
		System.out.println((int)Math.ceil(n * 1.0 / (2 * d  + 1)));
	}
} import java.util.*; util.* java import java.io.*; io.* java public class Main {
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt(), d = sc.nextInt();
		System.out.println((int)Math.ceil(n * 1.0 / (2 * d  + 1)));
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt(), d = sc.nextInt();
		System.out.println((int)Math.ceil(n * 1.0 / (2 * d  + 1)));
	} main {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt(), d = sc.nextInt();
		System.out.println((int)Math.ceil(n * 1.0 / (2 * d  + 1)));
	} 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 System.out.println((int)Math.ceil(n * 1.0 / (2 * d  + 1))) System.out.println System.out System System.out (int)Math.ceil(n * 1.0 / (2 * d  + 1)) Math.ceil Math n * 1.0 / (2 * d  + 1) n * 1.0 n 1.0 (2 * d  + 1) 2 * d 2 d 1 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();
		System.out.println((int)Math.ceil(n * 1.0 / (2 * d  + 1)));
	}
} public class Main {
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt(), d = sc.nextInt();
		System.out.println((int)Math.ceil(n * 1.0 / (2 * d  + 1)));
	}
} Main
import java.util.*;
import java.io.*;

public class Main {
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt(), d = sc.nextInt();
		System.out.println((int)Math.ceil(n * 1.0 / (2 * d  + 1)));
	}
}
