
import java.util.Scanner;

public class Main {

	Scanner scan = new Scanner(System.in);
	
	void compute() {
		int n = scan.nextInt();
		int d = scan.nextInt();
		
		System.out.println(n % (d * 2 + 1) == 0 ? n / (d * 2 + 1) : n / (d * 2 + 1) + 1);
	}
	
	
	public static void main(String...arg) {
		new Main().compute();
	}
}

/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