import java.io.BufferedReader;
		import java.io.IOException;
		import java.io.InputStreamReader;
import java.util.ArrayList;

public class Main {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		String[] nums = (br.readLine().split(" "));
		double num1 = Integer.parseInt(nums[0]);
		double num2 = Integer.parseInt(nums[1]);

		System.out.println((int)Math.ceil(num1/(num2*2+1)));
	}
} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.ArrayList; ArrayList java.util public class Main {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		String[] nums = (br.readLine().split(" "));
		double num1 = Integer.parseInt(nums[0]);
		double num2 = Integer.parseInt(nums[1]);

		System.out.println((int)Math.ceil(num1/(num2*2+1)));
	}
} Main public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		String[] nums = (br.readLine().split(" "));
		double num1 = Integer.parseInt(nums[0]);
		double num2 = Integer.parseInt(nums[1]);

		System.out.println((int)Math.ceil(num1/(num2*2+1)));
	} main {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		String[] nums = (br.readLine().split(" "));
		double num1 = Integer.parseInt(nums[0]);
		double num2 = Integer.parseInt(nums[1]);

		System.out.println((int)Math.ceil(num1/(num2*2+1)));
	} BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) String[] nums = (br.readLine().split(" ")); nums (br.readLine().split(" ")) br.readLine().split br.readLine() br.readLine br " " double num1 = Integer.parseInt(nums[0]); num1 Integer.parseInt(nums[0]) Integer.parseInt Integer nums[0] nums 0 double num2 = Integer.parseInt(nums[1]); num2 Integer.parseInt(nums[1]) Integer.parseInt Integer nums[1] nums 1 System.out.println((int)Math.ceil(num1/(num2*2+1))) System.out.println System.out System System.out (int)Math.ceil(num1/(num2*2+1)) Math.ceil Math num1/(num2*2+1) num1 (num2*2+1) num2*2 num2 2 1 String[] args args public class Main {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		String[] nums = (br.readLine().split(" "));
		double num1 = Integer.parseInt(nums[0]);
		double num2 = Integer.parseInt(nums[1]);

		System.out.println((int)Math.ceil(num1/(num2*2+1)));
	}
} public class Main {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		String[] nums = (br.readLine().split(" "));
		double num1 = Integer.parseInt(nums[0]);
		double num2 = Integer.parseInt(nums[1]);

		System.out.println((int)Math.ceil(num1/(num2*2+1)));
	}
} Main
import java.io.BufferedReader;
		import java.io.IOException;
		import java.io.InputStreamReader;
import java.util.ArrayList;

public class Main {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		String[] nums = (br.readLine().split(" "));
		double num1 = Integer.parseInt(nums[0]);
		double num2 = Integer.parseInt(nums[1]);

		System.out.println((int)Math.ceil(num1/(num2*2+1)));
	}
}
