import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println((int) Math.ceil(sc.nextDouble() / (2 * sc.nextInt() + 1)));
  }
} import java.util.Scanner; Scanner java.util public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println((int) Math.ceil(sc.nextDouble() / (2 * sc.nextInt() + 1)));
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println((int) Math.ceil(sc.nextDouble() / (2 * sc.nextInt() + 1)));
  } main {
    Scanner sc = new Scanner(System.in);
    System.out.println((int) Math.ceil(sc.nextDouble() / (2 * sc.nextInt() + 1)));
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) System.out.println((int) Math.ceil(sc.nextDouble() / (2 * sc.nextInt() + 1))) System.out.println System.out System System.out (int) Math.ceil(sc.nextDouble() / (2 * sc.nextInt() + 1)) Math.ceil Math sc.nextDouble() / (2 * sc.nextInt() + 1) sc.nextDouble() sc.nextDouble sc (2 * sc.nextInt() + 1) 2 * sc.nextInt() 2 sc.nextInt() sc.nextInt sc 1 String[] args args public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println((int) Math.ceil(sc.nextDouble() / (2 * sc.nextInt() + 1)));
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println((int) Math.ceil(sc.nextDouble() / (2 * sc.nextInt() + 1)));
  }
} Main
import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println((int) Math.ceil(sc.nextDouble() / (2 * sc.nextInt() + 1)));
  }
}