

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

public class Main {

	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		
		String[] tmpArray = br.readLine().split(" ");
		
		int n = Integer.parseInt(tmpArray[0]);
		int d = Integer.parseInt(tmpArray[1]);
		
		int result = n / (2*d + 1);
		
		if(n % (2*d + 1) != 0){
			result++;
		}
		System.out.println(result);
	}

} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io public class Main {

	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		
		String[] tmpArray = br.readLine().split(" ");
		
		int n = Integer.parseInt(tmpArray[0]);
		int d = Integer.parseInt(tmpArray[1]);
		
		int result = n / (2*d + 1);
		
		if(n % (2*d + 1) != 0){
			result++;
		}
		System.out.println(result);
	}

} Main /**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		
		String[] tmpArray = br.readLine().split(" ");
		
		int n = Integer.parseInt(tmpArray[0]);
		int d = Integer.parseInt(tmpArray[1]);
		
		int result = n / (2*d + 1);
		
		if(n % (2*d + 1) != 0){
			result++;
		}
		System.out.println(result);
	} main {
		// TODO Auto-generated method stub
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		
		String[] tmpArray = br.readLine().split(" ");
		
		int n = Integer.parseInt(tmpArray[0]);
		int d = Integer.parseInt(tmpArray[1]);
		
		int result = n / (2*d + 1);
		
		if(n % (2*d + 1) != 0){
			result++;
		}
		System.out.println(result);
	} BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) String[] tmpArray = br.readLine().split(" "); tmpArray br.readLine().split(" ") br.readLine().split br.readLine() br.readLine br " " int n = Integer.parseInt(tmpArray[0]); n Integer.parseInt(tmpArray[0]) Integer.parseInt Integer tmpArray[0] tmpArray 0 int d = Integer.parseInt(tmpArray[1]); d Integer.parseInt(tmpArray[1]) Integer.parseInt Integer tmpArray[1] tmpArray 1 int result = n / (2*d + 1); result n / (2*d + 1) n (2*d + 1) 2*d 2 d 1 if(n % (2*d + 1) != 0){
			result++;
		} n % (2*d + 1) != 0 n % (2*d + 1) n (2*d + 1) 2*d 2 d 1 0 {
			result++;
		} result++ result System.out.println(result) System.out.println System.out System System.out result String[] args args public class Main {

	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		
		String[] tmpArray = br.readLine().split(" ");
		
		int n = Integer.parseInt(tmpArray[0]);
		int d = Integer.parseInt(tmpArray[1]);
		
		int result = n / (2*d + 1);
		
		if(n % (2*d + 1) != 0){
			result++;
		}
		System.out.println(result);
	}

} public class Main {

	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		
		String[] tmpArray = br.readLine().split(" ");
		
		int n = Integer.parseInt(tmpArray[0]);
		int d = Integer.parseInt(tmpArray[1]);
		
		int result = n / (2*d + 1);
		
		if(n % (2*d + 1) != 0){
			result++;
		}
		System.out.println(result);
	}

} Main


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

public class Main {

	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		
		String[] tmpArray = br.readLine().split(" ");
		
		int n = Integer.parseInt(tmpArray[0]);
		int d = Integer.parseInt(tmpArray[1]);
		
		int result = n / (2*d + 1);
		
		if(n % (2*d + 1) != 0){
			result++;
		}
		System.out.println(result);
	}

}
