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());
        float result = N / (2f * D + 1);
        System.out.println((int) Math.ceil(result));
    }
} 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());
        float result = N / (2f * D + 1);
        System.out.println((int) Math.ceil(result));
    }
} 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());
        float result = N / (2f * D + 1);
        System.out.println((int) Math.ceil(result));
    } main {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        int D = Integer.parseInt(sc.next());
        float result = N / (2f * D + 1);
        System.out.println((int) Math.ceil(result));
    } 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 float result = N / (2f * D + 1); result N / (2f * D + 1) N (2f * D + 1) 2f * D 2f D 1 System.out.println((int) Math.ceil(result)) System.out.println System.out System System.out (int) Math.ceil(result) Math.ceil Math result 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());
        float result = N / (2f * D + 1);
        System.out.println((int) Math.ceil(result));
    }
} 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());
        float result = N / (2f * D + 1);
        System.out.println((int) Math.ceil(result));
    }
} 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());
        float result = N / (2f * D + 1);
        System.out.println((int) Math.ceil(result));
    }
}