import java.util.*;

public class Main {
    public static void main(String args[]){

        Scanner sc = new Scanner(System.in);

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

        int ans = n/(2*d+1);

        if (n%(2*d+1)==0){
            System.out.println(ans);
        }else{
            System.out.println(ans+1);
        }



    }
} import java.util.*; util.* 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 ans = n/(2*d+1);

        if (n%(2*d+1)==0){
            System.out.println(ans);
        }else{
            System.out.println(ans+1);
        }



    }
} Main public static void main(String args[]){

        Scanner sc = new Scanner(System.in);

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

        int ans = n/(2*d+1);

        if (n%(2*d+1)==0){
            System.out.println(ans);
        }else{
            System.out.println(ans+1);
        }



    } main {

        Scanner sc = new Scanner(System.in);

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

        int ans = n/(2*d+1);

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

        int ans = n/(2*d+1);

        if (n%(2*d+1)==0){
            System.out.println(ans);
        }else{
            System.out.println(ans+1);
        }



    }
} public class Main {
    public static void main(String args[]){

        Scanner sc = new Scanner(System.in);

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

        int ans = n/(2*d+1);

        if (n%(2*d+1)==0){
            System.out.println(ans);
        }else{
            System.out.println(ans+1);
        }



    }
} Main
import java.util.*;

public class Main {
    public static void main(String args[]){

        Scanner sc = new Scanner(System.in);

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

        int ans = n/(2*d+1);

        if (n%(2*d+1)==0){
            System.out.println(ans);
        }else{
            System.out.println(ans+1);
        }



    }
}
