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 k =D*2+1;
        
        if(N%k==0){
        System.out.print(N/k);
        }else{
        System.out.print(N/k+1);    
        }
}
} 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 k =D*2+1;
        
        if(N%k==0){
        System.out.print(N/k);
        }else{
        System.out.print(N/k+1);    
        }
}
} Main public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		
        int k =D*2+1;
        
        if(N%k==0){
        System.out.print(N/k);
        }else{
        System.out.print(N/k+1);    
        }
} main {
    
    Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		
        int k =D*2+1;
        
        if(N%k==0){
        System.out.print(N/k);
        }else{
        System.out.print(N/k+1);    
        }
} 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 k =D*2+1; k D*2+1 D*2 D 2 1 if(N%k==0){
        System.out.print(N/k);
        }else{
        System.out.print(N/k+1);    
        } N%k==0 N%k N k 0 {
        System.out.print(N/k);
        } System.out.print(N/k) System.out.print System.out System System.out N/k N k {
        System.out.print(N/k+1);    
        } System.out.print(N/k+1) System.out.print System.out System System.out N/k+1 N/k N k 1 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 k =D*2+1;
        
        if(N%k==0){
        System.out.print(N/k);
        }else{
        System.out.print(N/k+1);    
        }
}
} public class Main {
	public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		
        int k =D*2+1;
        
        if(N%k==0){
        System.out.print(N/k);
        }else{
        System.out.print(N/k+1);    
        }
}
} 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 k =D*2+1;
        
        if(N%k==0){
        System.out.print(N/k);
        }else{
        System.out.print(N/k+1);    
        }
}
}
