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

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

public class Main
{
	public static void main(String [] Args)
	{
		Scanner in=new Scanner(System.in);
		int n=in.nextInt();
		int d=in.nextInt();
		System.out.println((n-1)/(2*d+1)+1);
	}
}
	