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