import java.util.Scanner;

public class Main {
	Scanner scan = new Scanner(System.in);
	
	
	void compute() {
		int N = scan.nextInt();
		int D = scan.nextInt();
		double x = (double)N / (double)(2 * D + 1);
		int y = N / (2 * D + 1);
		if(0 < x - y) {
			y++;
		}
		System.out.println(y);
	}

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

} import java.util.Scanner; Scanner java.util public class Main {
	Scanner scan = new Scanner(System.in);
	
	
	void compute() {
		int N = scan.nextInt();
		int D = scan.nextInt();
		double x = (double)N / (double)(2 * D + 1);
		int y = N / (2 * D + 1);
		if(0 < x - y) {
			y++;
		}
		System.out.println(y);
	}

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

} Main Scanner scan = new Scanner(System.in); scan new Scanner(System.in) void compute() {
		int N = scan.nextInt();
		int D = scan.nextInt();
		double x = (double)N / (double)(2 * D + 1);
		int y = N / (2 * D + 1);
		if(0 < x - y) {
			y++;
		}
		System.out.println(y);
	} compute {
		int N = scan.nextInt();
		int D = scan.nextInt();
		double x = (double)N / (double)(2 * D + 1);
		int y = N / (2 * D + 1);
		if(0 < x - y) {
			y++;
		}
		System.out.println(y);
	} int N = scan.nextInt(); N scan.nextInt() scan.nextInt scan int D = scan.nextInt(); D scan.nextInt() scan.nextInt scan double x = (double)N / (double)(2 * D + 1); x (double)N / (double)(2 * D + 1) (double)N (double)(2 * D + 1) 2 * D 2 D 1 int y = N / (2 * D + 1); y N / (2 * D + 1) N (2 * D + 1) 2 * D 2 D 1 if(0 < x - y) {
			y++;
		} 0 < x - y 0 x - y x y {
			y++;
		} y++ y System.out.println(y) System.out.println System.out System System.out y public static void main(String[] args) {
		new Main().compute();
	} main {
		new Main().compute();
	} new Main().compute() new Main().compute new Main() String[] args args public class Main {
	Scanner scan = new Scanner(System.in);
	
	
	void compute() {
		int N = scan.nextInt();
		int D = scan.nextInt();
		double x = (double)N / (double)(2 * D + 1);
		int y = N / (2 * D + 1);
		if(0 < x - y) {
			y++;
		}
		System.out.println(y);
	}

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

} public class Main {
	Scanner scan = new Scanner(System.in);
	
	
	void compute() {
		int N = scan.nextInt();
		int D = scan.nextInt();
		double x = (double)N / (double)(2 * D + 1);
		int y = N / (2 * D + 1);
		if(0 < x - y) {
			y++;
		}
		System.out.println(y);
	}

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

} Main
import java.util.Scanner;

public class Main {
	Scanner scan = new Scanner(System.in);
	
	
	void compute() {
		int N = scan.nextInt();
		int D = scan.nextInt();
		double x = (double)N / (double)(2 * D + 1);
		int y = N / (2 * D + 1);
		if(0 < x - y) {
			y++;
		}
		System.out.println(y);
	}

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

}
