import java.util.*;

public class Main {
	Scanner sc;
	int N, D;
	
//=============
// constructor
//
	public Main() {
		sc = new Scanner(System.in);
	}
	
//==================
// instance methods
//
	void out(Object o) {
		System.out.println(o);
		System.out.flush();
	}
	
	public void exec() throws Exception {
		N = sc.nextInt();
		D = sc.nextInt();
		
		int n = (N+2*D) / (2*D+1);
		out(n);
	}
	
//======
// main
//
	public static void main(String[] args) throws Exception {
		Main m = new Main();
		m.exec();
	}

}
/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