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 rem = N % (2 * D + 1);
    int at = N / (2 * D + 1);
    if (rem > 0) {
      at++;
    }
    System.out.println(at);
  }
} 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 rem = N % (2 * D + 1);
    int at = N / (2 * D + 1);
    if (rem > 0) {
      at++;
    }
    System.out.println(at);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int D = sc.nextInt();
    int rem = N % (2 * D + 1);
    int at = N / (2 * D + 1);
    if (rem > 0) {
      at++;
    }
    System.out.println(at);
  } main {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int D = sc.nextInt();
    int rem = N % (2 * D + 1);
    int at = N / (2 * D + 1);
    if (rem > 0) {
      at++;
    }
    System.out.println(at);
  } 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 rem = N % (2 * D + 1); rem N % (2 * D + 1) N (2 * D + 1) 2 * D 2 D 1 int at = N / (2 * D + 1); at N / (2 * D + 1) N (2 * D + 1) 2 * D 2 D 1 if (rem > 0) {
      at++;
    } rem > 0 rem 0 {
      at++;
    } at++ at System.out.println(at) System.out.println System.out System System.out at 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 rem = N % (2 * D + 1);
    int at = N / (2 * D + 1);
    if (rem > 0) {
      at++;
    }
    System.out.println(at);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int D = sc.nextInt();
    int rem = N % (2 * D + 1);
    int at = N / (2 * D + 1);
    if (rem > 0) {
      at++;
    }
    System.out.println(at);
  }
} 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 rem = N % (2 * D + 1);
    int at = N / (2 * D + 1);
    if (rem > 0) {
      at++;
    }
    System.out.println(at);
  }
}
