import java.util.*;
public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		double N = sc.nextDouble();
		double D = sc.nextDouble();
		System.out.println((int)Math.ceil(N / ((2 * D) + 1)));
	}
} import java.util.*; util.* java public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		double N = sc.nextDouble();
		double D = sc.nextDouble();
		System.out.println((int)Math.ceil(N / ((2 * D) + 1)));
	}
} Main public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		double N = sc.nextDouble();
		double D = sc.nextDouble();
		System.out.println((int)Math.ceil(N / ((2 * D) + 1)));
	} main {
		Scanner sc = new Scanner(System.in);
		double N = sc.nextDouble();
		double D = sc.nextDouble();
		System.out.println((int)Math.ceil(N / ((2 * D) + 1)));
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double N = sc.nextDouble(); N sc.nextDouble() sc.nextDouble sc double D = sc.nextDouble(); D sc.nextDouble() sc.nextDouble sc System.out.println((int)Math.ceil(N / ((2 * D) + 1))) System.out.println System.out System System.out (int)Math.ceil(N / ((2 * D) + 1)) Math.ceil Math N / ((2 * D) + 1) N ((2 * D) + 1) (2 * D) 2 D 1 String args[] args public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		double N = sc.nextDouble();
		double D = sc.nextDouble();
		System.out.println((int)Math.ceil(N / ((2 * D) + 1)));
	}
} public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		double N = sc.nextDouble();
		double D = sc.nextDouble();
		System.out.println((int)Math.ceil(N / ((2 * D) + 1)));
	}
} Main
import java.util.*;
public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		double N = sc.nextDouble();
		double D = sc.nextDouble();
		System.out.println((int)Math.ceil(N / ((2 * D) + 1)));
	}
}
