import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner scan = new java.util.Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        double a = (double) n / (d * 2 + 1);
        if(a % 1 != 0){
            System.out.println(n / (d * 2 + 1) + 1);
        }else{
            System.out.println(n / (d * 2 + 1));
        }
    }
} import java.util.*; util.* java public class Main{
    public static void main(String[] args){
        Scanner scan = new java.util.Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        double a = (double) n / (d * 2 + 1);
        if(a % 1 != 0){
            System.out.println(n / (d * 2 + 1) + 1);
        }else{
            System.out.println(n / (d * 2 + 1));
        }
    }
} Main public static void main(String[] args){
        Scanner scan = new java.util.Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        double a = (double) n / (d * 2 + 1);
        if(a % 1 != 0){
            System.out.println(n / (d * 2 + 1) + 1);
        }else{
            System.out.println(n / (d * 2 + 1));
        }
    } main {
        Scanner scan = new java.util.Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        double a = (double) n / (d * 2 + 1);
        if(a % 1 != 0){
            System.out.println(n / (d * 2 + 1) + 1);
        }else{
            System.out.println(n / (d * 2 + 1));
        }
    } Scanner scan = new java.util.Scanner(System.in); scan new java.util.Scanner(System.in) int n = scan.nextInt(); n scan.nextInt() scan.nextInt scan int d = scan.nextInt(); d scan.nextInt() scan.nextInt scan double a = (double) n / (d * 2 + 1); a (double) n / (d * 2 + 1) (double) n (d * 2 + 1) d * 2 d 2 1 if(a % 1 != 0){
            System.out.println(n / (d * 2 + 1) + 1);
        }else{
            System.out.println(n / (d * 2 + 1));
        } a % 1 != 0 a % 1 a 1 0 {
            System.out.println(n / (d * 2 + 1) + 1);
        } System.out.println(n / (d * 2 + 1) + 1) System.out.println System.out System System.out n / (d * 2 + 1) + 1 n / (d * 2 + 1) n (d * 2 + 1) d * 2 d 2 1 1 {
            System.out.println(n / (d * 2 + 1));
        } System.out.println(n / (d * 2 + 1)) System.out.println System.out System System.out n / (d * 2 + 1) n (d * 2 + 1) d * 2 d 2 1 String[] args args public class Main{
    public static void main(String[] args){
        Scanner scan = new java.util.Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        double a = (double) n / (d * 2 + 1);
        if(a % 1 != 0){
            System.out.println(n / (d * 2 + 1) + 1);
        }else{
            System.out.println(n / (d * 2 + 1));
        }
    }
} public class Main{
    public static void main(String[] args){
        Scanner scan = new java.util.Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        double a = (double) n / (d * 2 + 1);
        if(a % 1 != 0){
            System.out.println(n / (d * 2 + 1) + 1);
        }else{
            System.out.println(n / (d * 2 + 1));
        }
    }
} Main
import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner scan = new java.util.Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt();
        double a = (double) n / (d * 2 + 1);
        if(a % 1 != 0){
            System.out.println(n / (d * 2 + 1) + 1);
        }else{
            System.out.println(n / (d * 2 + 1));
        }
    }
}