import java.util.Scanner;

public class Main{
	
 public static void main(String[] args) {
	 Scanner sc=new Scanner(System.in);
	 int N=sc.nextInt(),D=sc.nextInt();
	 int count=0;
	 int index=0;
	 
	 while(true) {
		 if(index+(2*D+1)>=N) {
			 count++;
			 break;
		 }
		 else {
			 index+=(2*D+1);
			 count++;
		 }
	 }
	 System.out.println(count);
	 
 }
	


}

 import java.util.Scanner; Scanner java.util public class Main{
	
 public static void main(String[] args) {
	 Scanner sc=new Scanner(System.in);
	 int N=sc.nextInt(),D=sc.nextInt();
	 int count=0;
	 int index=0;
	 
	 while(true) {
		 if(index+(2*D+1)>=N) {
			 count++;
			 break;
		 }
		 else {
			 index+=(2*D+1);
			 count++;
		 }
	 }
	 System.out.println(count);
	 
 }
	


} Main public static void main(String[] args) {
	 Scanner sc=new Scanner(System.in);
	 int N=sc.nextInt(),D=sc.nextInt();
	 int count=0;
	 int index=0;
	 
	 while(true) {
		 if(index+(2*D+1)>=N) {
			 count++;
			 break;
		 }
		 else {
			 index+=(2*D+1);
			 count++;
		 }
	 }
	 System.out.println(count);
	 
 } main {
	 Scanner sc=new Scanner(System.in);
	 int N=sc.nextInt(),D=sc.nextInt();
	 int count=0;
	 int index=0;
	 
	 while(true) {
		 if(index+(2*D+1)>=N) {
			 count++;
			 break;
		 }
		 else {
			 index+=(2*D+1);
			 count++;
		 }
	 }
	 System.out.println(count);
	 
 } Scanner sc=new Scanner(System.in); sc new Scanner(System.in) int N=sc.nextInt() N sc.nextInt() sc.nextInt sc D=sc.nextInt(); D sc.nextInt() sc.nextInt sc int count=0; count 0 int index=0; index 0 while(true) {
		 if(index+(2*D+1)>=N) {
			 count++;
			 break;
		 }
		 else {
			 index+=(2*D+1);
			 count++;
		 }
	 } true {
		 if(index+(2*D+1)>=N) {
			 count++;
			 break;
		 }
		 else {
			 index+=(2*D+1);
			 count++;
		 }
	 } if(index+(2*D+1)>=N) {
			 count++;
			 break;
		 }
		 else {
			 index+=(2*D+1);
			 count++;
		 } index+(2*D+1)>=N index+(2*D+1) index (2*D+1) 2*D 2 D 1 N {
			 count++;
			 break;
		 } count++ count break; {
			 index+=(2*D+1);
			 count++;
		 } index+=(2*D+1) index (2*D+1) 2*D 2 D 1 count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main{
	
 public static void main(String[] args) {
	 Scanner sc=new Scanner(System.in);
	 int N=sc.nextInt(),D=sc.nextInt();
	 int count=0;
	 int index=0;
	 
	 while(true) {
		 if(index+(2*D+1)>=N) {
			 count++;
			 break;
		 }
		 else {
			 index+=(2*D+1);
			 count++;
		 }
	 }
	 System.out.println(count);
	 
 }
	


} public class Main{
	
 public static void main(String[] args) {
	 Scanner sc=new Scanner(System.in);
	 int N=sc.nextInt(),D=sc.nextInt();
	 int count=0;
	 int index=0;
	 
	 while(true) {
		 if(index+(2*D+1)>=N) {
			 count++;
			 break;
		 }
		 else {
			 index+=(2*D+1);
			 count++;
		 }
	 }
	 System.out.println(count);
	 
 }
	


} Main
import java.util.Scanner;

public class Main{
	
 public static void main(String[] args) {
	 Scanner sc=new Scanner(System.in);
	 int N=sc.nextInt(),D=sc.nextInt();
	 int count=0;
	 int index=0;
	 
	 while(true) {
		 if(index+(2*D+1)>=N) {
			 count++;
			 break;
		 }
		 else {
			 index+=(2*D+1);
			 count++;
		 }
	 }
	 System.out.println(count);
	 
 }
	


}


