import java.util.Scanner;

public class Main{

    public static void main(String args[]){

        Scanner scan = new Scanner(System.in);
        Integer n = Integer.parseInt(scan.next());
        Integer d = Integer.parseInt(scan.next());
 
        int x = n/(2*d+1);
        int mod = n%((2*d+1));

        if(mod == 0)
            System.out.println(n/(2*d+1));
        else
            System.out.println(n/(2*d+1)+1);
    }
} import java.util.Scanner; Scanner java.util public class Main{

    public static void main(String args[]){

        Scanner scan = new Scanner(System.in);
        Integer n = Integer.parseInt(scan.next());
        Integer d = Integer.parseInt(scan.next());
 
        int x = n/(2*d+1);
        int mod = n%((2*d+1));

        if(mod == 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 scan = new Scanner(System.in);
        Integer n = Integer.parseInt(scan.next());
        Integer d = Integer.parseInt(scan.next());
 
        int x = n/(2*d+1);
        int mod = n%((2*d+1));

        if(mod == 0)
            System.out.println(n/(2*d+1));
        else
            System.out.println(n/(2*d+1)+1);
    } main {

        Scanner scan = new Scanner(System.in);
        Integer n = Integer.parseInt(scan.next());
        Integer d = Integer.parseInt(scan.next());
 
        int x = n/(2*d+1);
        int mod = n%((2*d+1));

        if(mod == 0)
            System.out.println(n/(2*d+1));
        else
            System.out.println(n/(2*d+1)+1);
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) Integer n = Integer.parseInt(scan.next()); n Integer.parseInt(scan.next()) Integer.parseInt Integer scan.next() scan.next scan Integer d = Integer.parseInt(scan.next()); d Integer.parseInt(scan.next()) Integer.parseInt Integer scan.next() scan.next scan int x = n/(2*d+1); x n/(2*d+1) n (2*d+1) 2*d 2 d 1 int mod = n%((2*d+1)); mod n%((2*d+1)) n ((2*d+1)) 2*d 2 d 1 if(mod == 0)
            System.out.println(n/(2*d+1));
        else
            System.out.println(n/(2*d+1)+1); mod == 0 mod 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 scan = new Scanner(System.in);
        Integer n = Integer.parseInt(scan.next());
        Integer d = Integer.parseInt(scan.next());
 
        int x = n/(2*d+1);
        int mod = n%((2*d+1));

        if(mod == 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 scan = new Scanner(System.in);
        Integer n = Integer.parseInt(scan.next());
        Integer d = Integer.parseInt(scan.next());
 
        int x = n/(2*d+1);
        int mod = n%((2*d+1));

        if(mod == 0)
            System.out.println(n/(2*d+1));
        else
            System.out.println(n/(2*d+1)+1);
    }
} Main
import java.util.Scanner;

public class Main{

    public static void main(String args[]){

        Scanner scan = new Scanner(System.in);
        Integer n = Integer.parseInt(scan.next());
        Integer d = Integer.parseInt(scan.next());
 
        int x = n/(2*d+1);
        int mod = n%((2*d+1));

        if(mod == 0)
            System.out.println(n/(2*d+1));
        else
            System.out.println(n/(2*d+1)+1);
    }
}