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 = D + D + 1;
		int ans = 0;

		ans = N / a + 1;
		if (N % a == 0) ans--;

		System.out.println(ans);
	}
} 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 = D + D + 1;
		int ans = 0;

		ans = N / a + 1;
		if (N % a == 0) ans--;

		System.out.println(ans);
	}
} Main public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int D = sc.nextInt();

		int a = D + D + 1;
		int ans = 0;

		ans = N / a + 1;
		if (N % a == 0) ans--;

		System.out.println(ans);
	} main {

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int D = sc.nextInt();

		int a = D + D + 1;
		int ans = 0;

		ans = N / a + 1;
		if (N % a == 0) ans--;

		System.out.println(ans);
	} 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 = D + D + 1; a D + D + 1 D + D + 1 D D 1 int ans = 0; ans 0 ans = N / a + 1 ans N / a + 1 N / a N a 1 if (N % a == 0) ans--; N % a == 0 N % a N a 0 ans-- ans System.out.println(ans) System.out.println System.out System System.out ans 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 = D + D + 1;
		int ans = 0;

		ans = N / a + 1;
		if (N % a == 0) ans--;

		System.out.println(ans);
	}
} 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 = D + D + 1;
		int ans = 0;

		ans = N / a + 1;
		if (N % a == 0) ans--;

		System.out.println(ans);
	}
} 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 = D + D + 1;
		int ans = 0;

		ans = N / a + 1;
		if (N % a == 0) ans--;

		System.out.println(ans);
	}
}