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 d_2=d*2+1;
	if(n%d_2!=0) {
		System.out.println((n/d_2)+1);
	}else {
		System.out.println(n/d_2);
	}
}
} 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 d_2=d*2+1;
	if(n%d_2!=0) {
		System.out.println((n/d_2)+1);
	}else {
		System.out.println(n/d_2);
	}
}
} Main public static void main(String[] args) {
	Scanner sc=new Scanner(System.in);
	int n=sc.nextInt();
	int d=sc.nextInt();
	int d_2=d*2+1;
	if(n%d_2!=0) {
		System.out.println((n/d_2)+1);
	}else {
		System.out.println(n/d_2);
	}
} main {
	Scanner sc=new Scanner(System.in);
	int n=sc.nextInt();
	int d=sc.nextInt();
	int d_2=d*2+1;
	if(n%d_2!=0) {
		System.out.println((n/d_2)+1);
	}else {
		System.out.println(n/d_2);
	}
} 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 d_2=d*2+1; d_2 d*2+1 d*2 d 2 1 if(n%d_2!=0) {
		System.out.println((n/d_2)+1);
	}else {
		System.out.println(n/d_2);
	} n%d_2!=0 n%d_2 n d_2 0 {
		System.out.println((n/d_2)+1);
	} System.out.println((n/d_2)+1) System.out.println System.out System System.out (n/d_2)+1 (n/d_2) n d_2 1 {
		System.out.println(n/d_2);
	} System.out.println(n/d_2) System.out.println System.out System System.out n/d_2 n d_2 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 d_2=d*2+1;
	if(n%d_2!=0) {
		System.out.println((n/d_2)+1);
	}else {
		System.out.println(n/d_2);
	}
}
} public class Main {
public static void main(String[] args) {
	Scanner sc=new Scanner(System.in);
	int n=sc.nextInt();
	int d=sc.nextInt();
	int d_2=d*2+1;
	if(n%d_2!=0) {
		System.out.println((n/d_2)+1);
	}else {
		System.out.println(n/d_2);
	}
}
} 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 d_2=d*2+1;
	if(n%d_2!=0) {
		System.out.println((n/d_2)+1);
	}else {
		System.out.println(n/d_2);
	}
}
}