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[] kns=new int[N];
		for(int i=0;i<N;i++){
			kns[i]=0;
		}
		int j=0;
		int sum=0;
		while(sum<N){
			sum+=1+2*D;
			j++;
		}
		System.out.println(j);
	}

}	 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[] kns=new int[N];
		for(int i=0;i<N;i++){
			kns[i]=0;
		}
		int j=0;
		int sum=0;
		while(sum<N){
			sum+=1+2*D;
			j++;
		}
		System.out.println(j);
	}

} Main public static void main(String[] args){
		Scanner sc=new Scanner(System.in);	
		
		int N=sc.nextInt();
		int D=sc.nextInt();
		
		int[] kns=new int[N];
		for(int i=0;i<N;i++){
			kns[i]=0;
		}
		int j=0;
		int sum=0;
		while(sum<N){
			sum+=1+2*D;
			j++;
		}
		System.out.println(j);
	} main {
		Scanner sc=new Scanner(System.in);	
		
		int N=sc.nextInt();
		int D=sc.nextInt();
		
		int[] kns=new int[N];
		for(int i=0;i<N;i++){
			kns[i]=0;
		}
		int j=0;
		int sum=0;
		while(sum<N){
			sum+=1+2*D;
			j++;
		}
		System.out.println(j);
	} 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[] kns=new int[N]; kns new int[N] N for(int i=0;i<N;i++){
			kns[i]=0;
		} int i=0; int i=0; i 0 i<N i N i++ i++ i {
			kns[i]=0;
		} {
			kns[i]=0;
		} kns[i]=0 kns[i] kns i 0 int j=0; j 0 int sum=0; sum 0 while(sum<N){
			sum+=1+2*D;
			j++;
		} sum<N sum N {
			sum+=1+2*D;
			j++;
		} sum+=1+2*D sum 1+2*D 1 2*D 2 D j++ j System.out.println(j) System.out.println System.out System System.out j 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[] kns=new int[N];
		for(int i=0;i<N;i++){
			kns[i]=0;
		}
		int j=0;
		int sum=0;
		while(sum<N){
			sum+=1+2*D;
			j++;
		}
		System.out.println(j);
	}

} public class Main{
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);	
		
		int N=sc.nextInt();
		int D=sc.nextInt();
		
		int[] kns=new int[N];
		for(int i=0;i<N;i++){
			kns[i]=0;
		}
		int j=0;
		int sum=0;
		while(sum<N){
			sum+=1+2*D;
			j++;
		}
		System.out.println(j);
	}

} 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[] kns=new int[N];
		for(int i=0;i<N;i++){
			kns[i]=0;
		}
		int j=0;
		int sum=0;
		while(sum<N){
			sum+=1+2*D;
			j++;
		}
		System.out.println(j);
	}

}	
