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();
        
        int m = 0;
        int n = 0;


        m = N/((D*2)+1);
        n = N%((D*2)+1);

        if(n != 0){
            m+=1;
        }

        if(D >= N){
            m = 1;
        }

        System.out.println(m);
        
    }

} 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();
        
        int m = 0;
        int n = 0;


        m = N/((D*2)+1);
        n = N%((D*2)+1);

        if(n != 0){
            m+=1;
        }

        if(D >= N){
            m = 1;
        }

        System.out.println(m);
        
    }

} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        
        int m = 0;
        int n = 0;


        m = N/((D*2)+1);
        n = N%((D*2)+1);

        if(n != 0){
            m+=1;
        }

        if(D >= N){
            m = 1;
        }

        System.out.println(m);
        
    } main {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        
        int m = 0;
        int n = 0;


        m = N/((D*2)+1);
        n = N%((D*2)+1);

        if(n != 0){
            m+=1;
        }

        if(D >= N){
            m = 1;
        }

        System.out.println(m);
        
    } 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 m = 0; m 0 int n = 0; n 0 m = N/((D*2)+1) m N/((D*2)+1) N ((D*2)+1) (D*2) D 2 1 n = N%((D*2)+1) n N%((D*2)+1) N ((D*2)+1) (D*2) D 2 1 if(n != 0){
            m+=1;
        } n != 0 n 0 {
            m+=1;
        } m+=1 m 1 if(D >= N){
            m = 1;
        } D >= N D N {
            m = 1;
        } m = 1 m 1 System.out.println(m) System.out.println System.out System System.out m 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();
        
        int m = 0;
        int n = 0;


        m = N/((D*2)+1);
        n = N%((D*2)+1);

        if(n != 0){
            m+=1;
        }

        if(D >= N){
            m = 1;
        }

        System.out.println(m);
        
    }

} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int D = sc.nextInt();
        
        int m = 0;
        int n = 0;


        m = N/((D*2)+1);
        n = N%((D*2)+1);

        if(n != 0){
            m+=1;
        }

        if(D >= N){
            m = 1;
        }

        System.out.println(m);
        
    }

} 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();
        
        int m = 0;
        int n = 0;


        m = N/((D*2)+1);
        n = N%((D*2)+1);

        if(n != 0){
            m+=1;
        }

        if(D >= N){
            m = 1;
        }

        System.out.println(m);
        
    }

}