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 res = N / ((2 * D) + 1);
        if (N % ((2 * D) + 1) != 0) {
            res++;
        }

        System.out.println(res);
    }
}
 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 res = N / ((2 * D) + 1);
        if (N % ((2 * D) + 1) != 0) {
            res++;
        }

        System.out.println(res);
    }
} 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 res = N / ((2 * D) + 1);
        if (N % ((2 * D) + 1) != 0) {
            res++;
        }

        System.out.println(res);
    } main {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        int D = Integer.parseInt(sc.next());

        int res = N / ((2 * D) + 1);
        if (N % ((2 * D) + 1) != 0) {
            res++;
        }

        System.out.println(res);
    } 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 res = N / ((2 * D) + 1); res N / ((2 * D) + 1) N ((2 * D) + 1) (2 * D) 2 D 1 if (N % ((2 * D) + 1) != 0) {
            res++;
        } N % ((2 * D) + 1) != 0 N % ((2 * D) + 1) N ((2 * D) + 1) (2 * D) 2 D 1 0 {
            res++;
        } res++ res System.out.println(res) System.out.println System.out System System.out res 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 res = N / ((2 * D) + 1);
        if (N % ((2 * D) + 1) != 0) {
            res++;
        }

        System.out.println(res);
    }
} 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 res = N / ((2 * D) + 1);
        if (N % ((2 * D) + 1) != 0) {
            res++;
        }

        System.out.println(res);
    }
} 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 res = N / ((2 * D) + 1);
        if (N % ((2 * D) + 1) != 0) {
            res++;
        }

        System.out.println(res);
    }
}

