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