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

public class Main{
public static void main (String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		if(n%(2*d+1) == 0)
		System.out.println(n/(2*d+1));
		else
		System.out.println(n/(2*d+1)+1);
}
} import java.util.*; util.* java import java.lang.*; lang.* 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();
		int d = sc.nextInt();
		if(n%(2*d+1) == 0)
		System.out.println(n/(2*d+1));
		else
		System.out.println(n/(2*d+1)+1);
}
} Main public static void main (String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		if(n%(2*d+1) == 0)
		System.out.println(n/(2*d+1));
		else
		System.out.println(n/(2*d+1)+1);
} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		if(n%(2*d+1) == 0)
		System.out.println(n/(2*d+1));
		else
		System.out.println(n/(2*d+1)+1);
} 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 if(n%(2*d+1) == 0)
		System.out.println(n/(2*d+1));
		else
		System.out.println(n/(2*d+1)+1); n%(2*d+1) == 0 n%(2*d+1) n (2*d+1) 2*d 2 d 1 0 System.out.println(n/(2*d+1)) System.out.println System.out System System.out n/(2*d+1) n (2*d+1) 2*d 2 d 1 System.out.println(n/(2*d+1)+1) System.out.println System.out System System.out n/(2*d+1)+1 n/(2*d+1) n (2*d+1) 2*d 2 d 1 1 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();
		if(n%(2*d+1) == 0)
		System.out.println(n/(2*d+1));
		else
		System.out.println(n/(2*d+1)+1);
}
} public class Main{
public static void main (String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		if(n%(2*d+1) == 0)
		System.out.println(n/(2*d+1));
		else
		System.out.println(n/(2*d+1)+1);
}
} Main
import java.util.*;
import java.lang.*;
import java.io.*;

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