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)));
	}
}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz