import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int number_n, number_d, count = 0;
    number_n = Integer.parseInt(sc.next());
    number_d = Integer.parseInt(sc.next());
    count = number_n / (2 * number_d + 1);
    if(number_n % (2 * number_d + 1) != 0) count++;
    System.out.println(count);
  }
} import java.util.*; util.* java public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int number_n, number_d, count = 0;
    number_n = Integer.parseInt(sc.next());
    number_d = Integer.parseInt(sc.next());
    count = number_n / (2 * number_d + 1);
    if(number_n % (2 * number_d + 1) != 0) count++;
    System.out.println(count);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int number_n, number_d, count = 0;
    number_n = Integer.parseInt(sc.next());
    number_d = Integer.parseInt(sc.next());
    count = number_n / (2 * number_d + 1);
    if(number_n % (2 * number_d + 1) != 0) count++;
    System.out.println(count);
  } main {
    Scanner sc = new Scanner(System.in);
    int number_n, number_d, count = 0;
    number_n = Integer.parseInt(sc.next());
    number_d = Integer.parseInt(sc.next());
    count = number_n / (2 * number_d + 1);
    if(number_n % (2 * number_d + 1) != 0) count++;
    System.out.println(count);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int number_n number_n number_d number_d count = 0; count 0 number_n = Integer.parseInt(sc.next()) number_n Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc number_d = Integer.parseInt(sc.next()) number_d Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc count = number_n / (2 * number_d + 1) count number_n / (2 * number_d + 1) number_n (2 * number_d + 1) 2 * number_d 2 number_d 1 if(number_n % (2 * number_d + 1) != 0) count++; number_n % (2 * number_d + 1) != 0 number_n % (2 * number_d + 1) number_n (2 * number_d + 1) 2 * number_d 2 number_d 1 0 count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int number_n, number_d, count = 0;
    number_n = Integer.parseInt(sc.next());
    number_d = Integer.parseInt(sc.next());
    count = number_n / (2 * number_d + 1);
    if(number_n % (2 * number_d + 1) != 0) count++;
    System.out.println(count);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int number_n, number_d, count = 0;
    number_n = Integer.parseInt(sc.next());
    number_d = Integer.parseInt(sc.next());
    count = number_n / (2 * number_d + 1);
    if(number_n % (2 * number_d + 1) != 0) count++;
    System.out.println(count);
  }
} Main
import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int number_n, number_d, count = 0;
    number_n = Integer.parseInt(sc.next());
    number_d = Integer.parseInt(sc.next());
    count = number_n / (2 * number_d + 1);
    if(number_n % (2 * number_d + 1) != 0) count++;
    System.out.println(count);
  }
}
