import 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 canWatch = 2*D +1;

        int result = N / canWatch;

        if(N % canWatch != 0) result++;

        System.out.println(result);

    }
} import java.util.*; util.* java public class Main {

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

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

        int canWatch = 2*D +1;

        int result = N / canWatch;

        if(N % canWatch != 0) result++;

        System.out.println(result);

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

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

        int canWatch = 2*D +1;

        int result = N / canWatch;

        if(N % canWatch != 0) result++;

        System.out.println(result);

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

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

        int canWatch = 2*D +1;

        int result = N / canWatch;

        if(N % canWatch != 0) result++;

        System.out.println(result);

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

        int result = N / canWatch;

        if(N % canWatch != 0) result++;

        System.out.println(result);

    }
} public class Main {

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

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

        int canWatch = 2*D +1;

        int result = N / canWatch;

        if(N % canWatch != 0) result++;

        System.out.println(result);

    }
} Main
import 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 canWatch = 2*D +1;

        int result = N / canWatch;

        if(N % canWatch != 0) result++;

        System.out.println(result);

    }
}
