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 ans = (int)Math.ceil(N / ((D * 2)+1.0));
        System.out.println(ans);
    }
} 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 ans = (int)Math.ceil(N / ((D * 2)+1.0));
        System.out.println(ans);
    }
} 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 ans = (int)Math.ceil(N / ((D * 2)+1.0));
        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        int D =  Integer.parseInt(sc.next());
        int ans = (int)Math.ceil(N / ((D * 2)+1.0));
        System.out.println(ans);
    } 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 ans = (int)Math.ceil(N / ((D * 2)+1.0)); ans (int)Math.ceil(N / ((D * 2)+1.0)) Math.ceil Math N / ((D * 2)+1.0) N ((D * 2)+1.0) (D * 2) D 2 1.0 System.out.println(ans) System.out.println System.out System System.out ans 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 ans = (int)Math.ceil(N / ((D * 2)+1.0));
        System.out.println(ans);
    }
} 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 ans = (int)Math.ceil(N / ((D * 2)+1.0));
        System.out.println(ans);
    }
} 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 ans = (int)Math.ceil(N / ((D * 2)+1.0));
        System.out.println(ans);
    }
}