import java.util.Scanner;

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

		int N = scanner.nextInt();
		int D = scanner.nextInt();
		while(1 > N || N > 20 || 1 > D || D > 20) {
			N = scanner.nextInt();
			D = scanner.nextInt();
		}

		int count = 1; // 必要な人の数
		int spot = D + 1; // 人のいる場所14

		while(spot + D + 1 <= N) {
			spot = spot + (2*D + 1);
			count++;
		}
		System.out.println(count);
		scanner.close();
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		int N = scanner.nextInt();
		int D = scanner.nextInt();
		while(1 > N || N > 20 || 1 > D || D > 20) {
			N = scanner.nextInt();
			D = scanner.nextInt();
		}

		int count = 1; // 必要な人の数
		int spot = D + 1; // 人のいる場所14

		while(spot + D + 1 <= N) {
			spot = spot + (2*D + 1);
			count++;
		}
		System.out.println(count);
		scanner.close();
	}
} Main public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		int N = scanner.nextInt();
		int D = scanner.nextInt();
		while(1 > N || N > 20 || 1 > D || D > 20) {
			N = scanner.nextInt();
			D = scanner.nextInt();
		}

		int count = 1; // 必要な人の数
		int spot = D + 1; // 人のいる場所14

		while(spot + D + 1 <= N) {
			spot = spot + (2*D + 1);
			count++;
		}
		System.out.println(count);
		scanner.close();
	} main {
		Scanner scanner = new Scanner(System.in);

		int N = scanner.nextInt();
		int D = scanner.nextInt();
		while(1 > N || N > 20 || 1 > D || D > 20) {
			N = scanner.nextInt();
			D = scanner.nextInt();
		}

		int count = 1; // 必要な人の数
		int spot = D + 1; // 人のいる場所14

		while(spot + D + 1 <= N) {
			spot = spot + (2*D + 1);
			count++;
		}
		System.out.println(count);
		scanner.close();
	} Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int N = scanner.nextInt(); N scanner.nextInt() scanner.nextInt scanner int D = scanner.nextInt(); D scanner.nextInt() scanner.nextInt scanner while(1 > N || N > 20 || 1 > D || D > 20) {
			N = scanner.nextInt();
			D = scanner.nextInt();
		} 1 > N || N > 20 || 1 > D || D > 20 1 > D 1 > N || N > 20 || 1 > D || D > 20 1 > N 1 N N > 20 N 20 1 > D 1 D D > 20 D 20 {
			N = scanner.nextInt();
			D = scanner.nextInt();
		} N = scanner.nextInt() N scanner.nextInt() scanner.nextInt scanner D = scanner.nextInt() D scanner.nextInt() scanner.nextInt scanner int count = 1; count 1 int spot = D + 1; spot D + 1 D 1 while(spot + D + 1 <= N) {
			spot = spot + (2*D + 1);
			count++;
		} spot + D + 1 <= N spot + D + 1 spot + D + 1 spot D 1 N {
			spot = spot + (2*D + 1);
			count++;
		} spot = spot + (2*D + 1) spot spot + (2*D + 1) spot (2*D + 1) 2*D 2 D 1 count++ count System.out.println(count) System.out.println System.out System System.out count scanner.close() scanner.close scanner String[] args args public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		int N = scanner.nextInt();
		int D = scanner.nextInt();
		while(1 > N || N > 20 || 1 > D || D > 20) {
			N = scanner.nextInt();
			D = scanner.nextInt();
		}

		int count = 1; // 必要な人の数
		int spot = D + 1; // 人のいる場所14

		while(spot + D + 1 <= N) {
			spot = spot + (2*D + 1);
			count++;
		}
		System.out.println(count);
		scanner.close();
	}
} public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		int N = scanner.nextInt();
		int D = scanner.nextInt();
		while(1 > N || N > 20 || 1 > D || D > 20) {
			N = scanner.nextInt();
			D = scanner.nextInt();
		}

		int count = 1; // 必要な人の数
		int spot = D + 1; // 人のいる場所14

		while(spot + D + 1 <= N) {
			spot = spot + (2*D + 1);
			count++;
		}
		System.out.println(count);
		scanner.close();
	}
} Main
import java.util.Scanner;

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

		int N = scanner.nextInt();
		int D = scanner.nextInt();
		while(1 > N || N > 20 || 1 > D || D > 20) {
			N = scanner.nextInt();
			D = scanner.nextInt();
		}

		int count = 1; // 必要な人の数
		int spot = D + 1; // 人のいる場所14

		while(spot + D + 1 <= N) {
			spot = spot + (2*D + 1);
			count++;
		}
		System.out.println(count);
		scanner.close();
	}
}
