import java.util.*;
 
public class Main{
	public static void main(String[] args){
    	Scanner scan = new Scanner(System.in);
      	int n = scan.nextInt();
      	int d = scan.nextInt();
      	int sight = 2 * d + 1;
      	int ans = (n / sight) ;
      	if(n % sight == 0) {
        	System.out.print(ans);
        }
      	else {
        	System.out.print(ans + 1);
        }
    }
} import java.util.*; util.* java public class Main{
	public static void main(String[] args){
    	Scanner scan = new Scanner(System.in);
      	int n = scan.nextInt();
      	int d = scan.nextInt();
      	int sight = 2 * d + 1;
      	int ans = (n / sight) ;
      	if(n % sight == 0) {
        	System.out.print(ans);
        }
      	else {
        	System.out.print(ans + 1);
        }
    }
} Main public static void main(String[] args){
    	Scanner scan = new Scanner(System.in);
      	int n = scan.nextInt();
      	int d = scan.nextInt();
      	int sight = 2 * d + 1;
      	int ans = (n / sight) ;
      	if(n % sight == 0) {
        	System.out.print(ans);
        }
      	else {
        	System.out.print(ans + 1);
        }
    } main {
    	Scanner scan = new Scanner(System.in);
      	int n = scan.nextInt();
      	int d = scan.nextInt();
      	int sight = 2 * d + 1;
      	int ans = (n / sight) ;
      	if(n % sight == 0) {
        	System.out.print(ans);
        }
      	else {
        	System.out.print(ans + 1);
        }
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int n = scan.nextInt(); n scan.nextInt() scan.nextInt scan int d = scan.nextInt(); d scan.nextInt() scan.nextInt scan int sight = 2 * d + 1; sight 2 * d + 1 2 * d 2 d 1 int ans = (n / sight) ; ans (n / sight) n sight if(n % sight == 0) {
        	System.out.print(ans);
        }
      	else {
        	System.out.print(ans + 1);
        } n % sight == 0 n % sight n sight 0 {
        	System.out.print(ans);
        } System.out.print(ans) System.out.print System.out System System.out ans {
        	System.out.print(ans + 1);
        } System.out.print(ans + 1) System.out.print System.out System System.out ans + 1 ans 1 String[] args args public class Main{
	public static void main(String[] args){
    	Scanner scan = new Scanner(System.in);
      	int n = scan.nextInt();
      	int d = scan.nextInt();
      	int sight = 2 * d + 1;
      	int ans = (n / sight) ;
      	if(n % sight == 0) {
        	System.out.print(ans);
        }
      	else {
        	System.out.print(ans + 1);
        }
    }
} public class Main{
	public static void main(String[] args){
    	Scanner scan = new Scanner(System.in);
      	int n = scan.nextInt();
      	int d = scan.nextInt();
      	int sight = 2 * d + 1;
      	int ans = (n / sight) ;
      	if(n % sight == 0) {
        	System.out.print(ans);
        }
      	else {
        	System.out.print(ans + 1);
        }
    }
} Main
import java.util.*;
 
public class Main{
	public static void main(String[] args){
    	Scanner scan = new Scanner(System.in);
      	int n = scan.nextInt();
      	int d = scan.nextInt();
      	int sight = 2 * d + 1;
      	int ans = (n / sight) ;
      	if(n % sight == 0) {
        	System.out.print(ans);
        }
      	else {
        	System.out.print(ans + 1);
        }
    }
}