import java.util.*;
public class Main {
	Scanner sc = new Scanner(System.in);
	int a,b,c,d,e,f,k,l,m,n,x,y,z;
	int ans;
	String[] S;

	Main(){
		// 整数の入力
		n = sc.nextInt();
		d = sc.nextInt();

		// 出力
		System.out.println(n%(d*2+1)==0?n/(d*2+1):n/(d*2+1)+1);
	}

	public static void main(String[] args){
		new Main();
	}
} import java.util.*; util.* java public class Main {
	Scanner sc = new Scanner(System.in);
	int a,b,c,d,e,f,k,l,m,n,x,y,z;
	int ans;
	String[] S;

	Main(){
		// 整数の入力
		n = sc.nextInt();
		d = sc.nextInt();

		// 出力
		System.out.println(n%(d*2+1)==0?n/(d*2+1):n/(d*2+1)+1);
	}

	public static void main(String[] args){
		new Main();
	}
} Main Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a a b b c c d d e e f f k k l l m m n n x x y y z; z int ans; ans String[] S; S Main(){
		// 整数の入力
		n = sc.nextInt();
		d = sc.nextInt();

		// 出力
		System.out.println(n%(d*2+1)==0?n/(d*2+1):n/(d*2+1)+1);
	} Main {
		// 整数の入力
		n = sc.nextInt();
		d = sc.nextInt();

		// 出力
		System.out.println(n%(d*2+1)==0?n/(d*2+1):n/(d*2+1)+1);
	} n = sc.nextInt() n sc.nextInt() sc.nextInt sc d = sc.nextInt() d sc.nextInt() sc.nextInt sc System.out.println(n%(d*2+1)==0?n/(d*2+1):n/(d*2+1)+1) System.out.println System.out System System.out n%(d*2+1)==0?n/(d*2+1):n/(d*2+1)+1 n%(d*2+1)==0 n%(d*2+1) n (d*2+1) d*2 d 2 1 0 n/(d*2+1) n (d*2+1) d*2 d 2 1 n/(d*2+1)+1 n/(d*2+1) n (d*2+1) d*2 d 2 1 1 public static void main(String[] args){
		new Main();
	} main {
		new Main();
	} new Main() String[] args args public class Main {
	Scanner sc = new Scanner(System.in);
	int a,b,c,d,e,f,k,l,m,n,x,y,z;
	int ans;
	String[] S;

	Main(){
		// 整数の入力
		n = sc.nextInt();
		d = sc.nextInt();

		// 出力
		System.out.println(n%(d*2+1)==0?n/(d*2+1):n/(d*2+1)+1);
	}

	public static void main(String[] args){
		new Main();
	}
} public class Main {
	Scanner sc = new Scanner(System.in);
	int a,b,c,d,e,f,k,l,m,n,x,y,z;
	int ans;
	String[] S;

	Main(){
		// 整数の入力
		n = sc.nextInt();
		d = sc.nextInt();

		// 出力
		System.out.println(n%(d*2+1)==0?n/(d*2+1):n/(d*2+1)+1);
	}

	public static void main(String[] args){
		new Main();
	}
} Main
import java.util.*;
public class Main {
	Scanner sc = new Scanner(System.in);
	int a,b,c,d,e,f,k,l,m,n,x,y,z;
	int ans;
	String[] S;

	Main(){
		// 整数の入力
		n = sc.nextInt();
		d = sc.nextInt();

		// 出力
		System.out.println(n%(d*2+1)==0?n/(d*2+1):n/(d*2+1)+1);
	}

	public static void main(String[] args){
		new Main();
	}
}