import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Solve s= new Solve();
		s.solve();
	}

}
class Solve{
	 Scanner sc = new Scanner(System.in) ;
	 void solve() {
		
		 int N =sc.nextInt();
		 int D =sc.nextInt();
		 int judge_sum =0;
		 int res = 0;
		 
		while(judge_sum<N) {
			res++;
			judge_sum+=2*D+1;
		}
		 
		 System.out.println(res);
	 }
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {

		Solve s= new Solve();
		s.solve();
	}

} Main public static void main(String[] args) {

		Solve s= new Solve();
		s.solve();
	} main {

		Solve s= new Solve();
		s.solve();
	} Solve s= new Solve(); s new Solve() s.solve() s.solve s String[] args args class Solve{
	 Scanner sc = new Scanner(System.in) ;
	 void solve() {
		
		 int N =sc.nextInt();
		 int D =sc.nextInt();
		 int judge_sum =0;
		 int res = 0;
		 
		while(judge_sum<N) {
			res++;
			judge_sum+=2*D+1;
		}
		 
		 System.out.println(res);
	 }
} Solve Scanner sc = new Scanner(System.in) ; sc new Scanner(System.in) void solve() {
		
		 int N =sc.nextInt();
		 int D =sc.nextInt();
		 int judge_sum =0;
		 int res = 0;
		 
		while(judge_sum<N) {
			res++;
			judge_sum+=2*D+1;
		}
		 
		 System.out.println(res);
	 } solve {
		
		 int N =sc.nextInt();
		 int D =sc.nextInt();
		 int judge_sum =0;
		 int res = 0;
		 
		while(judge_sum<N) {
			res++;
			judge_sum+=2*D+1;
		}
		 
		 System.out.println(res);
	 } int N =sc.nextInt(); N sc.nextInt() sc.nextInt sc int D =sc.nextInt(); D sc.nextInt() sc.nextInt sc int judge_sum =0; judge_sum 0 int res = 0; res 0 while(judge_sum<N) {
			res++;
			judge_sum+=2*D+1;
		} judge_sum<N judge_sum N {
			res++;
			judge_sum+=2*D+1;
		} res++ res judge_sum+=2*D+1 judge_sum 2*D+1 2*D 2 D 1 System.out.println(res) System.out.println System.out System System.out res public class Main {

	public static void main(String[] args) {

		Solve s= new Solve();
		s.solve();
	}

} public class Main {

	public static void main(String[] args) {

		Solve s= new Solve();
		s.solve();
	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Solve s= new Solve();
		s.solve();
	}

}
class Solve{
	 Scanner sc = new Scanner(System.in) ;
	 void solve() {
		
		 int N =sc.nextInt();
		 int D =sc.nextInt();
		 int judge_sum =0;
		 int res = 0;
		 
		while(judge_sum<N) {
			res++;
			judge_sum+=2*D+1;
		}
		 
		 System.out.println(res);
	 }
}