import java.util.Scanner; 

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

    while (in.hasNext()) {
      int N = in.nextInt();
      int D = in.nextInt();
      int range = 2 * D + 1;
      int ans = N / range + (N % range != 0 ? 1 : 0);

      System.out.println(ans);
    }
  }
} import java.util.Scanner; Scanner java.util public class Main {
  public static void main (String[] args) {
    Scanner in = new Scanner(System.in);

    while (in.hasNext()) {
      int N = in.nextInt();
      int D = in.nextInt();
      int range = 2 * D + 1;
      int ans = N / range + (N % range != 0 ? 1 : 0);

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

    while (in.hasNext()) {
      int N = in.nextInt();
      int D = in.nextInt();
      int range = 2 * D + 1;
      int ans = N / range + (N % range != 0 ? 1 : 0);

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

    while (in.hasNext()) {
      int N = in.nextInt();
      int D = in.nextInt();
      int range = 2 * D + 1;
      int ans = N / range + (N % range != 0 ? 1 : 0);

      System.out.println(ans);
    }
  } Scanner in = new Scanner(System.in); in new Scanner(System.in) while (in.hasNext()) {
      int N = in.nextInt();
      int D = in.nextInt();
      int range = 2 * D + 1;
      int ans = N / range + (N % range != 0 ? 1 : 0);

      System.out.println(ans);
    } in.hasNext() in.hasNext in {
      int N = in.nextInt();
      int D = in.nextInt();
      int range = 2 * D + 1;
      int ans = N / range + (N % range != 0 ? 1 : 0);

      System.out.println(ans);
    } int N = in.nextInt(); N in.nextInt() in.nextInt in int D = in.nextInt(); D in.nextInt() in.nextInt in int range = 2 * D + 1; range 2 * D + 1 2 * D 2 D 1 int ans = N / range + (N % range != 0 ? 1 : 0); ans N / range + (N % range != 0 ? 1 : 0) N / range N range (N % range != 0 ? 1 : 0) N % range != 0 N % range N range 0 1 0 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 in = new Scanner(System.in);

    while (in.hasNext()) {
      int N = in.nextInt();
      int D = in.nextInt();
      int range = 2 * D + 1;
      int ans = N / range + (N % range != 0 ? 1 : 0);

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

    while (in.hasNext()) {
      int N = in.nextInt();
      int D = in.nextInt();
      int range = 2 * D + 1;
      int ans = N / range + (N % range != 0 ? 1 : 0);

      System.out.println(ans);
    }
  }
} Main
import java.util.Scanner; 

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

    while (in.hasNext()) {
      int N = in.nextInt();
      int D = in.nextInt();
      int range = 2 * D + 1;
      int ans = N / range + (N % range != 0 ? 1 : 0);

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