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 a = 0;
		
		do {
			a++;
			n--;
			
		} while (a * 2 * d < n);
		
		System.out.println(a);
		
		sc.close();
		
	}

} 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 a = 0;
		
		do {
			a++;
			n--;
			
		} while (a * 2 * d < n);
		
		System.out.println(a);
		
		sc.close();
		
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt();
		int d = sc.nextInt();
		
		int a = 0;
		
		do {
			a++;
			n--;
			
		} while (a * 2 * d < n);
		
		System.out.println(a);
		
		sc.close();
		
	} main {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt();
		int d = sc.nextInt();
		
		int a = 0;
		
		do {
			a++;
			n--;
			
		} while (a * 2 * d < n);
		
		System.out.println(a);
		
		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 a = 0; a 0 do {
			a++;
			n--;
			
		} while (a * 2 * d < n); a * 2 * d < n a * 2 * d a * 2 * d a 2 d n {
			a++;
			n--;
			
		} a++ a n-- n System.out.println(a) System.out.println System.out System System.out a sc.close() sc.close sc 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 a = 0;
		
		do {
			a++;
			n--;
			
		} while (a * 2 * d < n);
		
		System.out.println(a);
		
		sc.close();
		
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt();
		int d = sc.nextInt();
		
		int a = 0;
		
		do {
			a++;
			n--;
			
		} while (a * 2 * d < n);
		
		System.out.println(a);
		
		sc.close();
		
	}

} 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 a = 0;
		
		do {
			a++;
			n--;
			
		} while (a * 2 * d < n);
		
		System.out.println(a);
		
		sc.close();
		
	}

}