import java.util.Scanner;

public class Main{

  public static void main (String[] args){

    Scanner sc = new Scanner (System.in);

    int N = sc.nextInt();
    int D = sc.nextInt();
    
    int hani = D*2+1;
    
    int answer = N/hani;
    
    if (N%hani!=0){
      answer++;
    }
    
    System.out.println(answer);
  }
} import java.util.Scanner; Scanner java.util public class Main{

  public static void main (String[] args){

    Scanner sc = new Scanner (System.in);

    int N = sc.nextInt();
    int D = sc.nextInt();
    
    int hani = D*2+1;
    
    int answer = N/hani;
    
    if (N%hani!=0){
      answer++;
    }
    
    System.out.println(answer);
  }
} Main public static void main (String[] args){

    Scanner sc = new Scanner (System.in);

    int N = sc.nextInt();
    int D = sc.nextInt();
    
    int hani = D*2+1;
    
    int answer = N/hani;
    
    if (N%hani!=0){
      answer++;
    }
    
    System.out.println(answer);
  } main {

    Scanner sc = new Scanner (System.in);

    int N = sc.nextInt();
    int D = sc.nextInt();
    
    int hani = D*2+1;
    
    int answer = N/hani;
    
    if (N%hani!=0){
      answer++;
    }
    
    System.out.println(answer);
  } Scanner sc = new Scanner (System.in); sc new Scanner (System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int D = sc.nextInt(); D sc.nextInt() sc.nextInt sc int hani = D*2+1; hani D*2+1 D*2 D 2 1 int answer = N/hani; answer N/hani N hani if (N%hani!=0){
      answer++;
    } N%hani!=0 N%hani N hani 0 {
      answer++;
    } answer++ answer System.out.println(answer) System.out.println System.out System System.out answer String[] args args public class Main{

  public static void main (String[] args){

    Scanner sc = new Scanner (System.in);

    int N = sc.nextInt();
    int D = sc.nextInt();
    
    int hani = D*2+1;
    
    int answer = N/hani;
    
    if (N%hani!=0){
      answer++;
    }
    
    System.out.println(answer);
  }
} public class Main{

  public static void main (String[] args){

    Scanner sc = new Scanner (System.in);

    int N = sc.nextInt();
    int D = sc.nextInt();
    
    int hani = D*2+1;
    
    int answer = N/hani;
    
    if (N%hani!=0){
      answer++;
    }
    
    System.out.println(answer);
  }
} Main
import java.util.Scanner;

public class Main{

  public static void main (String[] args){

    Scanner sc = new Scanner (System.in);

    int N = sc.nextInt();
    int D = sc.nextInt();
    
    int hani = D*2+1;
    
    int answer = N/hani;
    
    if (N%hani!=0){
      answer++;
    }
    
    System.out.println(answer);
  }
}