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();

		int res = N/(2*D+1);
		
		if(N%(2*D+1)>0) {
			res++;
		}
		System.out.println(res);
	}

} 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();

		int res = N/(2*D+1);
		
		if(N%(2*D+1)>0) {
			res++;
		}
		System.out.println(res);
	}

} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int D = scan.nextInt();
		scan.close();

		int res = N/(2*D+1);
		
		if(N%(2*D+1)>0) {
			res++;
		}
		System.out.println(res);
	} main {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int D = scan.nextInt();
		scan.close();

		int res = N/(2*D+1);
		
		if(N%(2*D+1)>0) {
			res++;
		}
		System.out.println(res);
	} 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 int res = N/(2*D+1); res N/(2*D+1) N (2*D+1) 2*D 2 D 1 if(N%(2*D+1)>0) {
			res++;
		} N%(2*D+1)>0 N%(2*D+1) N (2*D+1) 2*D 2 D 1 0 {
			res++;
		} res++ res System.out.println(res) System.out.println System.out System System.out res 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();

		int res = N/(2*D+1);
		
		if(N%(2*D+1)>0) {
			res++;
		}
		System.out.println(res);
	}

} 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();

		int res = N/(2*D+1);
		
		if(N%(2*D+1)>0) {
			res++;
		}
		System.out.println(res);
	}

} 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();

		int res = N/(2*D+1);
		
		if(N%(2*D+1)>0) {
			res++;
		}
		System.out.println(res);
	}

}