import java.io.BufferedReader;
import java.io.*;
import java.util.*;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Collections;

public class Main {
	public static void main(final String[] args){
    
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int d = sc.nextInt();

        int sv = 2 * d + 1;

        if(n % sv == 0){
            System.out.println(n / sv);
        }else{
            System.out.println(n / sv + 1);
        }
        
        

        






    }
} import java.io.BufferedReader; BufferedReader java.io import java.io.*; io.* java import java.util.*; util.* java import java.util.ArrayList; ArrayList java.util import java.util.Iterator; Iterator java.util import java.util.List; List java.util import java.util.Collections; Collections java.util public class Main {
	public static void main(final String[] args){
    
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int d = sc.nextInt();

        int sv = 2 * d + 1;

        if(n % sv == 0){
            System.out.println(n / sv);
        }else{
            System.out.println(n / sv + 1);
        }
        
        

        






    }
} Main public static void main(final String[] args){
    
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int d = sc.nextInt();

        int sv = 2 * d + 1;

        if(n % sv == 0){
            System.out.println(n / sv);
        }else{
            System.out.println(n / sv + 1);
        }
        
        

        






    } main {
    
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int d = sc.nextInt();

        int sv = 2 * d + 1;

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

        int n = sc.nextInt();
        int d = sc.nextInt();

        int sv = 2 * d + 1;

        if(n % sv == 0){
            System.out.println(n / sv);
        }else{
            System.out.println(n / sv + 1);
        }
        
        

        






    }
} public class Main {
	public static void main(final String[] args){
    
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int d = sc.nextInt();

        int sv = 2 * d + 1;

        if(n % sv == 0){
            System.out.println(n / sv);
        }else{
            System.out.println(n / sv + 1);
        }
        
        

        






    }
} Main
import java.io.BufferedReader;
import java.io.*;
import java.util.*;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Collections;

public class Main {
	public static void main(final String[] args){
    
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int d = sc.nextInt();

        int sv = 2 * d + 1;

        if(n % sv == 0){
            System.out.println(n / sv);
        }else{
            System.out.println(n / sv + 1);
        }
        
        

        






    }
}