import java.util.Scanner;

public class Main {
	public static void main(String args[]){

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();

		int length = d * 2 + 1;

		System.out.println(Math.round(Math.ceil((double)n / (double)length)));
	}
} import java.util.Scanner; Scanner 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();

		int length = d * 2 + 1;

		System.out.println(Math.round(Math.ceil((double)n / (double)length)));
	}
} Main public static void main(String args[]){

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();

		int length = d * 2 + 1;

		System.out.println(Math.round(Math.ceil((double)n / (double)length)));
	} main {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();

		int length = d * 2 + 1;

		System.out.println(Math.round(Math.ceil((double)n / (double)length)));
	} 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 int length = d * 2 + 1; length d * 2 + 1 d * 2 d 2 1 System.out.println(Math.round(Math.ceil((double)n / (double)length))) System.out.println System.out System System.out Math.round(Math.ceil((double)n / (double)length)) Math.round Math Math.ceil((double)n / (double)length) Math.ceil Math (double)n / (double)length (double)n (double)length 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();

		int length = d * 2 + 1;

		System.out.println(Math.round(Math.ceil((double)n / (double)length)));
	}
} public class Main {
	public static void main(String args[]){

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();

		int length = d * 2 + 1;

		System.out.println(Math.round(Math.ceil((double)n / (double)length)));
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String args[]){

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();

		int length = d * 2 + 1;

		System.out.println(Math.round(Math.ceil((double)n / (double)length)));
	}
}
