import 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 a = d*2+1;
    int b = n%a==0 ? n/a:n/a+1;   
    System.out.println(b);
  } 
} import java.util.*; util.* java public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int a = d*2+1;
    int b = n%a==0 ? n/a:n/a+1;   
    System.out.println(b);
  } 
} Main public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int a = d*2+1;
    int b = n%a==0 ? n/a:n/a+1;   
    System.out.println(b);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int a = d*2+1;
    int b = n%a==0 ? n/a:n/a+1;   
    System.out.println(b);
  } 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 a = d*2+1; a d*2+1 d*2 d 2 1 int b = n%a==0 ? n/a:n/a+1; b n%a==0 ? n/a:n/a+1 n%a==0 n%a n a 0 n/a n a n/a+1 n/a n a 1 System.out.println(b) System.out.println System.out System System.out b 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 a = d*2+1;
    int b = n%a==0 ? n/a:n/a+1;   
    System.out.println(b);
  } 
} public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int a = d*2+1;
    int b = n%a==0 ? n/a:n/a+1;   
    System.out.println(b);
  } 
} Main
import 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 a = d*2+1;
    int b = n%a==0 ? n/a:n/a+1;   
    System.out.println(b);
  } 
}