import java.util.Scanner;

public class Main{
	public static void main(String[]args) {
		
		Scanner sc=new Scanner(System.in);
		
		int N=sc.nextInt();
		int D=sc.nextInt();
		
		int num=N-2*D-2;
		
		if(2*D+1>=N) {
			System.out.println(1);
		}else {
		int x=(int)Math.ceil(num/(2*D+1));
		System.out.println(x+2);
		}
		sc.close();
	}
} import java.util.Scanner; Scanner java.util public class Main{
	public static void main(String[]args) {
		
		Scanner sc=new Scanner(System.in);
		
		int N=sc.nextInt();
		int D=sc.nextInt();
		
		int num=N-2*D-2;
		
		if(2*D+1>=N) {
			System.out.println(1);
		}else {
		int x=(int)Math.ceil(num/(2*D+1));
		System.out.println(x+2);
		}
		sc.close();
	}
} Main public static void main(String[]args) {
		
		Scanner sc=new Scanner(System.in);
		
		int N=sc.nextInt();
		int D=sc.nextInt();
		
		int num=N-2*D-2;
		
		if(2*D+1>=N) {
			System.out.println(1);
		}else {
		int x=(int)Math.ceil(num/(2*D+1));
		System.out.println(x+2);
		}
		sc.close();
	} main {
		
		Scanner sc=new Scanner(System.in);
		
		int N=sc.nextInt();
		int D=sc.nextInt();
		
		int num=N-2*D-2;
		
		if(2*D+1>=N) {
			System.out.println(1);
		}else {
		int x=(int)Math.ceil(num/(2*D+1));
		System.out.println(x+2);
		}
		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 int num=N-2*D-2; num N-2*D-2 N-2*D-2 N 2*D 2 D 2 if(2*D+1>=N) {
			System.out.println(1);
		}else {
		int x=(int)Math.ceil(num/(2*D+1));
		System.out.println(x+2);
		} 2*D+1>=N 2*D+1 2*D 2 D 1 N {
			System.out.println(1);
		} System.out.println(1) System.out.println System.out System System.out 1 {
		int x=(int)Math.ceil(num/(2*D+1));
		System.out.println(x+2);
		} int x=(int)Math.ceil(num/(2*D+1)); x (int)Math.ceil(num/(2*D+1)) Math.ceil Math num/(2*D+1) num (2*D+1) 2*D 2 D 1 System.out.println(x+2) System.out.println System.out System System.out x+2 x 2 sc.close() sc.close sc 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 num=N-2*D-2;
		
		if(2*D+1>=N) {
			System.out.println(1);
		}else {
		int x=(int)Math.ceil(num/(2*D+1));
		System.out.println(x+2);
		}
		sc.close();
	}
} public class Main{
	public static void main(String[]args) {
		
		Scanner sc=new Scanner(System.in);
		
		int N=sc.nextInt();
		int D=sc.nextInt();
		
		int num=N-2*D-2;
		
		if(2*D+1>=N) {
			System.out.println(1);
		}else {
		int x=(int)Math.ceil(num/(2*D+1));
		System.out.println(x+2);
		}
		sc.close();
	}
} Main
import java.util.Scanner;

public class Main{
	public static void main(String[]args) {
		
		Scanner sc=new Scanner(System.in);
		
		int N=sc.nextInt();
		int D=sc.nextInt();
		
		int num=N-2*D-2;
		
		if(2*D+1>=N) {
			System.out.println(1);
		}else {
		int x=(int)Math.ceil(num/(2*D+1));
		System.out.println(x+2);
		}
		sc.close();
	}
}