import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n=scan.nextInt();
		int d=scan.nextInt();
		scan.close();

		System.out.println((n%(d*2+1)!=0)? n/(d*2+1)+1:n/(d*2+1));
	}
} import java.util.Scanner; Scanner 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();
		scan.close();

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

		System.out.println((n%(d*2+1)!=0)? n/(d*2+1)+1:n/(d*2+1));
	} main {
		Scanner scan = new Scanner(System.in);
		int n=scan.nextInt();
		int d=scan.nextInt();
		scan.close();

		System.out.println((n%(d*2+1)!=0)? n/(d*2+1)+1:n/(d*2+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 scan.close() scan.close scan System.out.println((n%(d*2+1)!=0)? n/(d*2+1)+1:n/(d*2+1)) System.out.println System.out System System.out (n%(d*2+1)!=0)? n/(d*2+1)+1:n/(d*2+1) (n%(d*2+1)!=0) n%(d*2+1) n (d*2+1) d*2 d 2 1 0 n/(d*2+1)+1 n/(d*2+1) n (d*2+1) d*2 d 2 1 1 n/(d*2+1) n (d*2+1) d*2 d 2 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();
		scan.close();

		System.out.println((n%(d*2+1)!=0)? n/(d*2+1)+1:n/(d*2+1));
	}
} public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n=scan.nextInt();
		int d=scan.nextInt();
		scan.close();

		System.out.println((n%(d*2+1)!=0)? n/(d*2+1)+1:n/(d*2+1));
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n=scan.nextInt();
		int d=scan.nextInt();
		scan.close();

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