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

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int ans = 0;			
		int search = d * 2 + 1;
		
		ans = n / search;
		if (n % search > 0)
		ans++;
		out.println(ans);
	}
} import java.util.*; util.* 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) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int ans = 0;			
		int search = d * 2 + 1;
		
		ans = n / search;
		if (n % search > 0)
		ans++;
		out.println(ans);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int ans = 0;			
		int search = d * 2 + 1;
		
		ans = n / search;
		if (n % search > 0)
		ans++;
		out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int ans = 0;			
		int search = d * 2 + 1;
		
		ans = n / search;
		if (n % search > 0)
		ans++;
		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 int ans = 0; ans 0 int search = d * 2 + 1; search d * 2 + 1 d * 2 d 2 1 ans = n / search ans n / search n search if (n % search > 0)
		ans++; n % search > 0 n % search n search 0 ans++ ans out.println(ans) out.println 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();
		int ans = 0;			
		int search = d * 2 + 1;
		
		ans = n / search;
		if (n % search > 0)
		ans++;
		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();
		int ans = 0;			
		int search = d * 2 + 1;
		
		ans = n / search;
		if (n % search > 0)
		ans++;
		out.println(ans);
	}
} Main
import java.util.*;
import static java.lang.System.*;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		int ans = 0;			
		int search = d * 2 + 1;
		
		ans = n / search;
		if (n % search > 0)
		ans++;
		out.println(ans);
	}
}