import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		double N = sc.nextInt(),D = sc.nextInt();
		System.out.print((int)(Math.ceil(N/(D*2+1))));

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

	}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		double N = sc.nextInt(),D = sc.nextInt();
		System.out.print((int)(Math.ceil(N/(D*2+1))));

	} main {
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		double N = sc.nextInt(),D = sc.nextInt();
		System.out.print((int)(Math.ceil(N/(D*2+1))));

	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double N = sc.nextInt() N sc.nextInt() sc.nextInt sc D = sc.nextInt(); D sc.nextInt() sc.nextInt sc System.out.print((int)(Math.ceil(N/(D*2+1)))) System.out.print System.out System System.out (int)(Math.ceil(N/(D*2+1))) Math.ceil Math 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 sc = new Scanner(System.in);
		// 整数の入力
		double N = sc.nextInt(),D = sc.nextInt();
		System.out.print((int)(Math.ceil(N/(D*2+1))));

	}
} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		double N = sc.nextInt(),D = sc.nextInt();
		System.out.print((int)(Math.ceil(N/(D*2+1))));

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

	}
}