import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N, D, a, ans;
		N = sc.nextInt();
		D = sc.nextInt();
		sc.close();
		a = 0;
		ans = 0;
		while (N > a) {
			a += 2 * D + 1;
			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, D, a, ans;
		N = sc.nextInt();
		D = sc.nextInt();
		sc.close();
		a = 0;
		ans = 0;
		while (N > a) {
			a += 2 * D + 1;
			ans++;
		}
		System.out.println(ans);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N, D, a, ans;
		N = sc.nextInt();
		D = sc.nextInt();
		sc.close();
		a = 0;
		ans = 0;
		while (N > a) {
			a += 2 * D + 1;
			ans++;
		}
		System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		int N, D, a, ans;
		N = sc.nextInt();
		D = sc.nextInt();
		sc.close();
		a = 0;
		ans = 0;
		while (N > a) {
			a += 2 * D + 1;
			ans++;
		}
		System.out.println(ans);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N N D D a a ans; ans N = sc.nextInt() N sc.nextInt() sc.nextInt sc D = sc.nextInt() D sc.nextInt() sc.nextInt sc sc.close() sc.close sc a = 0 a 0 ans = 0 ans 0 while (N > a) {
			a += 2 * D + 1;
			ans++;
		} N > a N a {
			a += 2 * D + 1;
			ans++;
		} a += 2 * D + 1 a 2 * D + 1 2 * D 2 D 1 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, D, a, ans;
		N = sc.nextInt();
		D = sc.nextInt();
		sc.close();
		a = 0;
		ans = 0;
		while (N > a) {
			a += 2 * D + 1;
			ans++;
		}
		System.out.println(ans);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N, D, a, ans;
		N = sc.nextInt();
		D = sc.nextInt();
		sc.close();
		a = 0;
		ans = 0;
		while (N > a) {
			a += 2 * D + 1;
			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, D, a, ans;
		N = sc.nextInt();
		D = sc.nextInt();
		sc.close();
		a = 0;
		ans = 0;
		while (N > a) {
			a += 2 * D + 1;
			ans++;
		}
		System.out.println(ans);
	}
}
