import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		
		int n = in.nextInt();
		int d = in.nextInt();
		
		// 守備範囲
		d = d*2 +1;
		
		if(n%d == 0) {
			System.out.println(n/d);
		} else {
			System.out.println(n/d +1);
		}
		
		in.close();
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		
		int n = in.nextInt();
		int d = in.nextInt();
		
		// 守備範囲
		d = d*2 +1;
		
		if(n%d == 0) {
			System.out.println(n/d);
		} else {
			System.out.println(n/d +1);
		}
		
		in.close();
	}
} Main public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		
		int n = in.nextInt();
		int d = in.nextInt();
		
		// 守備範囲
		d = d*2 +1;
		
		if(n%d == 0) {
			System.out.println(n/d);
		} else {
			System.out.println(n/d +1);
		}
		
		in.close();
	} main {
		Scanner in = new Scanner(System.in);
		
		int n = in.nextInt();
		int d = in.nextInt();
		
		// 守備範囲
		d = d*2 +1;
		
		if(n%d == 0) {
			System.out.println(n/d);
		} else {
			System.out.println(n/d +1);
		}
		
		in.close();
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) int n = in.nextInt(); n in.nextInt() in.nextInt in int d = in.nextInt(); d in.nextInt() in.nextInt in d = d*2 +1 d d*2 +1 d*2 d 2 1 if(n%d == 0) {
			System.out.println(n/d);
		} else {
			System.out.println(n/d +1);
		} n%d == 0 n%d n d 0 {
			System.out.println(n/d);
		} System.out.println(n/d) System.out.println System.out System System.out n/d n d {
			System.out.println(n/d +1);
		} System.out.println(n/d +1) System.out.println System.out System System.out n/d +1 n/d n d 1 in.close() in.close in String[] args args public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		
		int n = in.nextInt();
		int d = in.nextInt();
		
		// 守備範囲
		d = d*2 +1;
		
		if(n%d == 0) {
			System.out.println(n/d);
		} else {
			System.out.println(n/d +1);
		}
		
		in.close();
	}
} public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		
		int n = in.nextInt();
		int d = in.nextInt();
		
		// 守備範囲
		d = d*2 +1;
		
		if(n%d == 0) {
			System.out.println(n/d);
		} else {
			System.out.println(n/d +1);
		}
		
		in.close();
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		
		int n = in.nextInt();
		int d = in.nextInt();
		
		// 守備範囲
		d = d*2 +1;
		
		if(n%d == 0) {
			System.out.println(n/d);
		} else {
			System.out.println(n/d +1);
		}
		
		in.close();
	}
}
