import java.util.Scanner;

public class Main {

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

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

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

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

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

} public class Main {

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

} Main
import java.util.Scanner;

public class Main {

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

}