import java.util.*; 
 
class Main{
public static void main(String[] args){
	Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int d=sc.nextInt();
  		int c=0;
		int ans=0;
  
		while(c<n){
          c+=d*2+1;
          ans++;
    		
    	}
    
    	System.out.println(ans);
    }
} import java.util.*; util.* java class Main{
public static void main(String[] args){
	Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int d=sc.nextInt();
  		int c=0;
		int ans=0;
  
		while(c<n){
          c+=d*2+1;
          ans++;
    		
    	}
    
    	System.out.println(ans);
    }
} Main public static void main(String[] args){
	Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int d=sc.nextInt();
  		int c=0;
		int ans=0;
  
		while(c<n){
          c+=d*2+1;
          ans++;
    		
    	}
    
    	System.out.println(ans);
    } main {
	Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int d=sc.nextInt();
  		int c=0;
		int ans=0;
  
		while(c<n){
          c+=d*2+1;
          ans++;
    		
    	}
    
    	System.out.println(ans);
    } 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 c=0; c 0 int ans=0; ans 0 while(c<n){
          c+=d*2+1;
          ans++;
    		
    	} c<n c n {
          c+=d*2+1;
          ans++;
    		
    	} c+=d*2+1 c d*2+1 d*2 d 2 1 ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args
import java.util.*; 
 
class Main{
public static void main(String[] args){
	Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int d=sc.nextInt();
  		int c=0;
		int ans=0;
  
		while(c<n){
          c+=d*2+1;
          ans++;
    		
    	}
    
    	System.out.println(ans);
    }
}