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();

        int search = 2 * d + 1;
        int ans = 0;
        for (int i = 0; i < 20; i++) {
            if (n <= 0) {
                break;
            }
            n -= search;
            ans++;
        }

        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 = sc.nextInt();
        int d = sc.nextInt();

        int search = 2 * d + 1;
        int ans = 0;
        for (int i = 0; i < 20; i++) {
            if (n <= 0) {
                break;
            }
            n -= search;
            ans++;
        }

        System.out.println(ans);
    }
} Main public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int d = sc.nextInt();

        int search = 2 * d + 1;
        int ans = 0;
        for (int i = 0; i < 20; i++) {
            if (n <= 0) {
                break;
            }
            n -= search;
            ans++;
        }

        System.out.println(ans);
    } main {

        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int d = sc.nextInt();

        int search = 2 * d + 1;
        int ans = 0;
        for (int i = 0; i < 20; i++) {
            if (n <= 0) {
                break;
            }
            n -= search;
            ans++;
        }

        System.out.println(ans);
    } 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 int search = 2 * d + 1; search 2 * d + 1 2 * d 2 d 1 int ans = 0; ans 0 for (int i = 0; i < 20; i++) {
            if (n <= 0) {
                break;
            }
            n -= search;
            ans++;
        } int i = 0; int i = 0; i 0 i < 20 i 20 i++ i++ i {
            if (n <= 0) {
                break;
            }
            n -= search;
            ans++;
        } {
            if (n <= 0) {
                break;
            }
            n -= search;
            ans++;
        } if (n <= 0) {
                break;
            } n <= 0 n 0 {
                break;
            } break; n -= search n search ans++ ans 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 = sc.nextInt();
        int d = sc.nextInt();

        int search = 2 * d + 1;
        int ans = 0;
        for (int i = 0; i < 20; i++) {
            if (n <= 0) {
                break;
            }
            n -= search;
            ans++;
        }

        System.out.println(ans);
    }
} public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int d = sc.nextInt();

        int search = 2 * d + 1;
        int ans = 0;
        for (int i = 0; i < 20; i++) {
            if (n <= 0) {
                break;
            }
            n -= search;
            ans++;
        }

        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 = sc.nextInt();
        int d = sc.nextInt();

        int search = 2 * d + 1;
        int ans = 0;
        for (int i = 0; i < 20; i++) {
            if (n <= 0) {
                break;
            }
            n -= search;
            ans++;
        }

        System.out.println(ans);
    }
}
