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 ans = 0;
        for (int i = 0; i < n; i++) {
            ans++;
            i += d*2;
        }

        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 ans = 0;
        for (int i = 0; i < n; i++) {
            ans++;
            i += d*2;
        }

        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 ans = 0;
        for (int i = 0; i < n; i++) {
            ans++;
            i += d*2;
        }

        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);

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

        int ans = 0;
        for (int i = 0; i < n; i++) {
            ans++;
            i += d*2;
        }

        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 ans = 0; ans 0 for (int i = 0; i < n; i++) {
            ans++;
            i += d*2;
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            ans++;
            i += d*2;
        } {
            ans++;
            i += d*2;
        } ans++ ans i += d*2 i d*2 d 2 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 ans = 0;
        for (int i = 0; i < n; i++) {
            ans++;
            i += d*2;
        }

        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 ans = 0;
        for (int i = 0; i < n; i++) {
            ans++;
            i += d*2;
        }

        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 ans = 0;
        for (int i = 0; i < n; i++) {
            ans++;
            i += d*2;
        }

        System.out.println(ans);
    }
}