import java.util.*;

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

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

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

		int m = 2 * D + 1;
		System.out.println((int)Math.ceil((double)N / m));
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		sc.close();

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

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

		int m = 2 * D + 1;
		System.out.println((int)Math.ceil((double)N / m));
	}
} Main
import java.util.*;

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

		int m = 2 * D + 1;
		System.out.println((int)Math.ceil((double)N / m));
	}
}
