import java.util.*;
import java.util.Arrays;
public class Main{
    
    public static void main(String[] args){
       Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        System.out.println((int)Math.ceil((double)a/(double)(2*b+1)));
    }
   
    
       
    
} import java.util.*; util.* java import java.util.Arrays; Arrays java.util public class Main{
    
    public static void main(String[] args){
       Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        System.out.println((int)Math.ceil((double)a/(double)(2*b+1)));
    }
   
    
       
    
} Main public static void main(String[] args){
       Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        System.out.println((int)Math.ceil((double)a/(double)(2*b+1)));
    } main {
       Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        System.out.println((int)Math.ceil((double)a/(double)(2*b+1)));
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double a = sc.nextDouble(); a sc.nextDouble() sc.nextDouble sc double b = sc.nextDouble(); b sc.nextDouble() sc.nextDouble sc System.out.println((int)Math.ceil((double)a/(double)(2*b+1))) System.out.println System.out System System.out (int)Math.ceil((double)a/(double)(2*b+1)) Math.ceil Math (double)a/(double)(2*b+1) (double)a (double)(2*b+1) 2*b 2 b 1 String[] args args public class Main{
    
    public static void main(String[] args){
       Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        System.out.println((int)Math.ceil((double)a/(double)(2*b+1)));
    }
   
    
       
    
} public class Main{
    
    public static void main(String[] args){
       Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        System.out.println((int)Math.ceil((double)a/(double)(2*b+1)));
    }
   
    
       
    
} Main
import java.util.*;
import java.util.Arrays;
public class Main{
    
    public static void main(String[] args){
       Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        System.out.println((int)Math.ceil((double)a/(double)(2*b+1)));
    }
   
    
       
    
}