import java.util.Scanner;

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

		int n = sc.nextInt();
		int d = sc.nextInt();

		int scope = d * 2 + 1;
		int num = n % scope == 0 ? n / scope : n / scope + 1;

		System.out.println(num);

		sc.close();
	}

} import java.util.Scanner; Scanner java.util class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int d = sc.nextInt();

		int scope = d * 2 + 1;
		int num = n % scope == 0 ? n / scope : n / scope + 1;

		System.out.println(num);

		sc.close();
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int d = sc.nextInt();

		int scope = d * 2 + 1;
		int num = n % scope == 0 ? n / scope : n / scope + 1;

		System.out.println(num);

		sc.close();
	} main {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int d = sc.nextInt();

		int scope = d * 2 + 1;
		int num = n % scope == 0 ? n / scope : n / scope + 1;

		System.out.println(num);

		sc.close();
	} 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 scope = d * 2 + 1; scope d * 2 + 1 d * 2 d 2 1 int num = n % scope == 0 ? n / scope : n / scope + 1; num n % scope == 0 ? n / scope : n / scope + 1 n % scope == 0 n % scope n scope 0 n / scope n scope n / scope + 1 n / scope n scope 1 System.out.println(num) System.out.println System.out System System.out num sc.close() sc.close sc String[] args args
import java.util.Scanner;

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

		int n = sc.nextInt();
		int d = sc.nextInt();

		int scope = d * 2 + 1;
		int num = n % scope == 0 ? n / scope : n / scope + 1;

		System.out.println(num);

		sc.close();
	}

}
