import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        System.out.println(solve(N, D));

        sc.close();
    }

    static int solve(int N, int D) {
        return (N + D * 2) / (D * 2 + 1);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        System.out.println(solve(N, D));

        sc.close();
    }

    static int solve(int N, int D) {
        return (N + D * 2) / (D * 2 + 1);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        System.out.println(solve(N, D));

        sc.close();
    } main {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        System.out.println(solve(N, D));

        sc.close();
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int D = sc.nextInt(); D sc.nextInt() sc.nextInt sc System.out.println(solve(N, D)) System.out.println System.out System System.out solve(N, D) solve N D sc.close() sc.close sc String[] args args static int solve(int N, int D) {
        return (N + D * 2) / (D * 2 + 1);
    } solve {
        return (N + D * 2) / (D * 2 + 1);
    } return (N + D * 2) / (D * 2 + 1); (N + D * 2) / (D * 2 + 1) (N + D * 2) N D * 2 D 2 (D * 2 + 1) D * 2 D 2 1 int N N int D D public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        System.out.println(solve(N, D));

        sc.close();
    }

    static int solve(int N, int D) {
        return (N + D * 2) / (D * 2 + 1);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        System.out.println(solve(N, D));

        sc.close();
    }

    static int solve(int N, int D) {
        return (N + D * 2) / (D * 2 + 1);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int D = sc.nextInt();

        System.out.println(solve(N, D));

        sc.close();
    }

    static int solve(int N, int D) {
        return (N + D * 2) / (D * 2 + 1);
    }
}