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();

	if(N%(2*D+1) !=0) {
		System.out.print(N/(2*D+1) +1);
	}

	else {System.out.print(N/(2*D+1));}


}
} 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();

	if(N%(2*D+1) !=0) {
		System.out.print(N/(2*D+1) +1);
	}

	else {System.out.print(N/(2*D+1));}


}
} Main public static void main(String args[]) {
	Scanner sc = new Scanner(System.in);

	int N = sc.nextInt();

	int D = sc.nextInt();

	if(N%(2*D+1) !=0) {
		System.out.print(N/(2*D+1) +1);
	}

	else {System.out.print(N/(2*D+1));}


} main {
	Scanner sc = new Scanner(System.in);

	int N = sc.nextInt();

	int D = sc.nextInt();

	if(N%(2*D+1) !=0) {
		System.out.print(N/(2*D+1) +1);
	}

	else {System.out.print(N/(2*D+1));}


} 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 if(N%(2*D+1) !=0) {
		System.out.print(N/(2*D+1) +1);
	}

	else {System.out.print(N/(2*D+1));} N%(2*D+1) !=0 N%(2*D+1) N (2*D+1) 2*D 2 D 1 0 {
		System.out.print(N/(2*D+1) +1);
	} System.out.print(N/(2*D+1) +1) System.out.print System.out System System.out N/(2*D+1) +1 N/(2*D+1) N (2*D+1) 2*D 2 D 1 1 {System.out.print(N/(2*D+1));} System.out.print(N/(2*D+1)) System.out.print System.out System System.out N/(2*D+1) N (2*D+1) 2*D 2 D 1 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();

	if(N%(2*D+1) !=0) {
		System.out.print(N/(2*D+1) +1);
	}

	else {System.out.print(N/(2*D+1));}


}
} public class Main {
public static void main(String args[]) {
	Scanner sc = new Scanner(System.in);

	int N = sc.nextInt();

	int D = sc.nextInt();

	if(N%(2*D+1) !=0) {
		System.out.print(N/(2*D+1) +1);
	}

	else {System.out.print(N/(2*D+1));}


}
} 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();

	if(N%(2*D+1) !=0) {
		System.out.print(N/(2*D+1) +1);
	}

	else {System.out.print(N/(2*D+1));}


}
}