import java.util.Scanner;

//AtCoder Beginner Contest 134
//B	Golden Apple
public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		sc.close();

		int mod = N % (D * 2 + 1);
		int ans = N / (D * 2 + 1);
		if (mod != 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();
		sc.close();

		int mod = N % (D * 2 + 1);
		int ans = N / (D * 2 + 1);
		if (mod != 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();
		sc.close();

		int mod = N % (D * 2 + 1);
		int ans = N / (D * 2 + 1);
		if (mod != 0) {
			ans++;
		}

		System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		sc.close();

		int mod = N % (D * 2 + 1);
		int ans = N / (D * 2 + 1);
		if (mod != 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 sc.close() sc.close sc int mod = N % (D * 2 + 1); mod N % (D * 2 + 1) N (D * 2 + 1) D * 2 D 2 1 int ans = N / (D * 2 + 1); ans N / (D * 2 + 1) N (D * 2 + 1) D * 2 D 2 1 if (mod != 0) {
			ans++;
		} mod != 0 mod 0 {
			ans++;
		} 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();
		sc.close();

		int mod = N % (D * 2 + 1);
		int ans = N / (D * 2 + 1);
		if (mod != 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();
		sc.close();

		int mod = N % (D * 2 + 1);
		int ans = N / (D * 2 + 1);
		if (mod != 0) {
			ans++;
		}

		System.out.println(ans);
	}
} Main
import java.util.Scanner;

//AtCoder Beginner Contest 134
//B	Golden Apple
public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int D = sc.nextInt();
		sc.close();

		int mod = N % (D * 2 + 1);
		int ans = N / (D * 2 + 1);
		if (mod != 0) {
			ans++;
		}

		System.out.println(ans);
	}
}
