import java.util.*;

/**
 * Main
 */
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
		int D = sc.nextInt();

		if(N%(2*D+1)==0){
			System.out.println(N/(2*D+1));

		}else{
			System.out.println(N/(2*D+1)+1);
		}

		sc.close();
	}
}; import java.util.*; util.* java public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
		int D = sc.nextInt();

		if(N%(2*D+1)==0){
			System.out.println(N/(2*D+1));

		}else{
			System.out.println(N/(2*D+1)+1);
		}

		sc.close();
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
		int D = sc.nextInt();

		if(N%(2*D+1)==0){
			System.out.println(N/(2*D+1));

		}else{
			System.out.println(N/(2*D+1)+1);
		}

		sc.close();
	} main {
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
		int D = sc.nextInt();

		if(N%(2*D+1)==0){
			System.out.println(N/(2*D+1));

		}else{
			System.out.println(N/(2*D+1)+1);
		}

		sc.close();
	} 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 if(N%(2*D+1)==0){
			System.out.println(N/(2*D+1));

		}else{
			System.out.println(N/(2*D+1)+1);
		} N%(2*D+1)==0 N%(2*D+1) N (2*D+1) 2*D 2 D 1 0 {
			System.out.println(N/(2*D+1));

		} System.out.println(N/(2*D+1)) System.out.println System.out System System.out N/(2*D+1) N (2*D+1) 2*D 2 D 1 {
			System.out.println(N/(2*D+1)+1);
		} System.out.println(N/(2*D+1)+1) System.out.println System.out System System.out N/(2*D+1)+1 N/(2*D+1) N (2*D+1) 2*D 2 D 1 1 sc.close() sc.close sc String[] args args public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
		int D = sc.nextInt();

		if(N%(2*D+1)==0){
			System.out.println(N/(2*D+1));

		}else{
			System.out.println(N/(2*D+1)+1);
		}

		sc.close();
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
		int D = sc.nextInt();

		if(N%(2*D+1)==0){
			System.out.println(N/(2*D+1));

		}else{
			System.out.println(N/(2*D+1)+1);
		}

		sc.close();
	}
} Main
import java.util.*;

/**
 * Main
 */
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int N = sc.nextInt();
		int D = sc.nextInt();

		if(N%(2*D+1)==0){
			System.out.println(N/(2*D+1));

		}else{
			System.out.println(N/(2*D+1)+1);
		}

		sc.close();
	}
};
