/*
	submission # - User: herp_sy
	https://atcoder.jp/contests/
*/

import java.util.*;
import java.io.*;
import static java.lang.System.*;

public class Main{
	public static void main(String[] args){
		int n,d;
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		d = sc.nextInt();

		out.println((n + d * 2) / (d * 2 + 1));
	}
} import java.util.*; util.* java import java.io.*; io.* java import static java.lang.System.*; import static java.lang.System.*; import static java.lang.System.*; public class Main{
	public static void main(String[] args){
		int n,d;
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		d = sc.nextInt();

		out.println((n + d * 2) / (d * 2 + 1));
	}
} Main public static void main(String[] args){
		int n,d;
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		d = sc.nextInt();

		out.println((n + d * 2) / (d * 2 + 1));
	} main {
		int n,d;
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		d = sc.nextInt();

		out.println((n + d * 2) / (d * 2 + 1));
	} int n n d; d Scanner sc = new Scanner(System.in); sc new Scanner(System.in) n = sc.nextInt() n sc.nextInt() sc.nextInt sc d = sc.nextInt() d sc.nextInt() sc.nextInt sc out.println((n + d * 2) / (d * 2 + 1)) out.println out (n + d * 2) / (d * 2 + 1) (n + d * 2) n d * 2 d 2 (d * 2 + 1) d * 2 d 2 1 String[] args args public class Main{
	public static void main(String[] args){
		int n,d;
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		d = sc.nextInt();

		out.println((n + d * 2) / (d * 2 + 1));
	}
} public class Main{
	public static void main(String[] args){
		int n,d;
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		d = sc.nextInt();

		out.println((n + d * 2) / (d * 2 + 1));
	}
} Main
/*
	submission # - User: herp_sy
	https://atcoder.jp/contests/
*/

import java.util.*;
import java.io.*;
import static java.lang.System.*;

public class Main{
	public static void main(String[] args){
		int n,d;
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		d = sc.nextInt();

		out.println((n + d * 2) / (d * 2 + 1));
	}
}
