import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int d = Integer.parseInt(sc.next());
        int range = 2*d+1;
        System.out.println((n+range-1)/range);
        System.out.flush();
        sc.close();
    }

} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int d = Integer.parseInt(sc.next());
        int range = 2*d+1;
        System.out.println((n+range-1)/range);
        System.out.flush();
        sc.close();
    }

} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int d = Integer.parseInt(sc.next());
        int range = 2*d+1;
        System.out.println((n+range-1)/range);
        System.out.flush();
        sc.close();
    } main {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int d = Integer.parseInt(sc.next());
        int range = 2*d+1;
        System.out.println((n+range-1)/range);
        System.out.flush();
        sc.close();
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = Integer.parseInt(sc.next()); n Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int d = Integer.parseInt(sc.next()); d Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int range = 2*d+1; range 2*d+1 2*d 2 d 1 System.out.println((n+range-1)/range) System.out.println System.out System System.out (n+range-1)/range (n+range-1) n+range n range 1 range System.out.flush() System.out.flush System.out System System.out sc.close() sc.close sc String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int d = Integer.parseInt(sc.next());
        int range = 2*d+1;
        System.out.println((n+range-1)/range);
        System.out.flush();
        sc.close();
    }

} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int d = Integer.parseInt(sc.next());
        int range = 2*d+1;
        System.out.println((n+range-1)/range);
        System.out.flush();
        sc.close();
    }

} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int d = Integer.parseInt(sc.next());
        int range = 2*d+1;
        System.out.println((n+range-1)/range);
        System.out.flush();
        sc.close();
    }

}