import java.util.*;

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

public class Main{
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int d = scan.nextInt() * 2 + 1;
        System.out.println(n % d == 0 ? n / d : n / d + 1);
        scan.close();
    }
}