import java.util.*;

public class Main{
	public static void main(String args[]){
    	Scanner scanner = new Scanner(System.in);
        int tree = scanner.nextInt();
        int patrol_width = scanner.nextInt();
      
        int max_patrol = patrol_width * 2 + 1;
      
        for(int i = 1; i <= 20; i++){
            if(tree <= max_patrol * i){
			    System.out.println(i);
                break;
            }
        }
    }
} import java.util.*; util.* java public class Main{
	public static void main(String args[]){
    	Scanner scanner = new Scanner(System.in);
        int tree = scanner.nextInt();
        int patrol_width = scanner.nextInt();
      
        int max_patrol = patrol_width * 2 + 1;
      
        for(int i = 1; i <= 20; i++){
            if(tree <= max_patrol * i){
			    System.out.println(i);
                break;
            }
        }
    }
} Main public static void main(String args[]){
    	Scanner scanner = new Scanner(System.in);
        int tree = scanner.nextInt();
        int patrol_width = scanner.nextInt();
      
        int max_patrol = patrol_width * 2 + 1;
      
        for(int i = 1; i <= 20; i++){
            if(tree <= max_patrol * i){
			    System.out.println(i);
                break;
            }
        }
    } main {
    	Scanner scanner = new Scanner(System.in);
        int tree = scanner.nextInt();
        int patrol_width = scanner.nextInt();
      
        int max_patrol = patrol_width * 2 + 1;
      
        for(int i = 1; i <= 20; i++){
            if(tree <= max_patrol * i){
			    System.out.println(i);
                break;
            }
        }
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int tree = scanner.nextInt(); tree scanner.nextInt() scanner.nextInt scanner int patrol_width = scanner.nextInt(); patrol_width scanner.nextInt() scanner.nextInt scanner int max_patrol = patrol_width * 2 + 1; max_patrol patrol_width * 2 + 1 patrol_width * 2 patrol_width 2 1 for(int i = 1; i <= 20; i++){
            if(tree <= max_patrol * i){
			    System.out.println(i);
                break;
            }
        } int i = 1; int i = 1; i 1 i <= 20 i 20 i++ i++ i {
            if(tree <= max_patrol * i){
			    System.out.println(i);
                break;
            }
        } {
            if(tree <= max_patrol * i){
			    System.out.println(i);
                break;
            }
        } if(tree <= max_patrol * i){
			    System.out.println(i);
                break;
            } tree <= max_patrol * i tree max_patrol * i max_patrol i {
			    System.out.println(i);
                break;
            } System.out.println(i) System.out.println System.out System System.out i break; String args[] args public class Main{
	public static void main(String args[]){
    	Scanner scanner = new Scanner(System.in);
        int tree = scanner.nextInt();
        int patrol_width = scanner.nextInt();
      
        int max_patrol = patrol_width * 2 + 1;
      
        for(int i = 1; i <= 20; i++){
            if(tree <= max_patrol * i){
			    System.out.println(i);
                break;
            }
        }
    }
} public class Main{
	public static void main(String args[]){
    	Scanner scanner = new Scanner(System.in);
        int tree = scanner.nextInt();
        int patrol_width = scanner.nextInt();
      
        int max_patrol = patrol_width * 2 + 1;
      
        for(int i = 1; i <= 20; i++){
            if(tree <= max_patrol * i){
			    System.out.println(i);
                break;
            }
        }
    }
} Main
import java.util.*;

public class Main{
	public static void main(String args[]){
    	Scanner scanner = new Scanner(System.in);
        int tree = scanner.nextInt();
        int patrol_width = scanner.nextInt();
      
        int max_patrol = patrol_width * 2 + 1;
      
        for(int i = 1; i <= 20; i++){
            if(tree <= max_patrol * i){
			    System.out.println(i);
                break;
            }
        }
    }
}