import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		int n = in.nextInt();
		int d = in.nextInt();
		int x = 2 * d + 1;
		if (n % x == 0)
			System.out.println(n / x);
		else
			System.out.println(n / x + 1);
		in.close();
	}
} import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.ArrayList; ArrayList java.util import java.util.Arrays; Arrays java.util import java.util.Comparator; Comparator java.util import java.util.HashMap; HashMap java.util import java.util.Map; Map java.util import java.util.Scanner; Scanner java.util public class Main {

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

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

	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		int n = in.nextInt();
		int d = in.nextInt();
		int x = 2 * d + 1;
		if (n % x == 0)
			System.out.println(n / x);
		else
			System.out.println(n / x + 1);
		in.close();
	}
} Main
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		int n = in.nextInt();
		int d = in.nextInt();
		int x = 2 * d + 1;
		if (n % x == 0)
			System.out.println(n / x);
		else
			System.out.println(n / x + 1);
		in.close();
	}
}
