import java.util.Scanner;
public class Main {

		static void solve() {
			Scanner sc = new Scanner(System.in);
			double n = sc.nextDouble();
			double d = sc.nextDouble();
			System.out.println((int)Math.ceil(n/(d*2+1)));
			sc.close();
		}
	public static void main(String[] args) {
	solve();

	}

} import java.util.Scanner; Scanner java.util public class Main {

		static void solve() {
			Scanner sc = new Scanner(System.in);
			double n = sc.nextDouble();
			double d = sc.nextDouble();
			System.out.println((int)Math.ceil(n/(d*2+1)));
			sc.close();
		}
	public static void main(String[] args) {
	solve();

	}

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

	} main {
	solve();

	} solve() solve String[] args args public class Main {

		static void solve() {
			Scanner sc = new Scanner(System.in);
			double n = sc.nextDouble();
			double d = sc.nextDouble();
			System.out.println((int)Math.ceil(n/(d*2+1)));
			sc.close();
		}
	public static void main(String[] args) {
	solve();

	}

} public class Main {

		static void solve() {
			Scanner sc = new Scanner(System.in);
			double n = sc.nextDouble();
			double d = sc.nextDouble();
			System.out.println((int)Math.ceil(n/(d*2+1)));
			sc.close();
		}
	public static void main(String[] args) {
	solve();

	}

} Main
import java.util.Scanner;
public class Main {

		static void solve() {
			Scanner sc = new Scanner(System.in);
			double n = sc.nextDouble();
			double d = sc.nextDouble();
			System.out.println((int)Math.ceil(n/(d*2+1)));
			sc.close();
		}
	public static void main(String[] args) {
	solve();

	}

}
