import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int D = scan.nextInt();
		int b = N;
		int count=0;
		for(int i=1;b>0;i++) {
			if(i-D>=0) {
				b = b - ((i+D)-(i-D)+1);
				count++;
			}
		}
		System.out.println(count);
	}

} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int D = scan.nextInt();
		int b = N;
		int count=0;
		for(int i=1;b>0;i++) {
			if(i-D>=0) {
				b = b - ((i+D)-(i-D)+1);
				count++;
			}
		}
		System.out.println(count);
	}

} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int D = scan.nextInt();
		int b = N;
		int count=0;
		for(int i=1;b>0;i++) {
			if(i-D>=0) {
				b = b - ((i+D)-(i-D)+1);
				count++;
			}
		}
		System.out.println(count);
	} main {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int D = scan.nextInt();
		int b = N;
		int count=0;
		for(int i=1;b>0;i++) {
			if(i-D>=0) {
				b = b - ((i+D)-(i-D)+1);
				count++;
			}
		}
		System.out.println(count);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int N = scan.nextInt(); N scan.nextInt() scan.nextInt scan int D = scan.nextInt(); D scan.nextInt() scan.nextInt scan int b = N; b N int count=0; count 0 for(int i=1;b>0;i++) {
			if(i-D>=0) {
				b = b - ((i+D)-(i-D)+1);
				count++;
			}
		} int i=1; int i=1; i 1 b>0 b 0 i++ i++ i {
			if(i-D>=0) {
				b = b - ((i+D)-(i-D)+1);
				count++;
			}
		} {
			if(i-D>=0) {
				b = b - ((i+D)-(i-D)+1);
				count++;
			}
		} if(i-D>=0) {
				b = b - ((i+D)-(i-D)+1);
				count++;
			} i-D>=0 i-D i D 0 {
				b = b - ((i+D)-(i-D)+1);
				count++;
			} b = b - ((i+D)-(i-D)+1) b b - ((i+D)-(i-D)+1) b ((i+D)-(i-D)+1) (i+D)-(i-D) (i+D) i D (i-D) i D 1 count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int D = scan.nextInt();
		int b = N;
		int count=0;
		for(int i=1;b>0;i++) {
			if(i-D>=0) {
				b = b - ((i+D)-(i-D)+1);
				count++;
			}
		}
		System.out.println(count);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int D = scan.nextInt();
		int b = N;
		int count=0;
		for(int i=1;b>0;i++) {
			if(i-D>=0) {
				b = b - ((i+D)-(i-D)+1);
				count++;
			}
		}
		System.out.println(count);
	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int D = scan.nextInt();
		int b = N;
		int count=0;
		for(int i=1;b>0;i++) {
			if(i-D>=0) {
				b = b - ((i+D)-(i-D)+1);
				count++;
			}
		}
		System.out.println(count);
	}

}