import 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 answer = 0;
    
    answer = n/(2*d+1);
    if(n%(2*d+1)!=0){
      answer=answer+1;
    }
    System.out.println(answer);
  }
  

  
} import java.util.*; util.* java public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    
    int answer = 0;
    
    answer = n/(2*d+1);
    if(n%(2*d+1)!=0){
      answer=answer+1;
    }
    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 answer = 0;
    
    answer = n/(2*d+1);
    if(n%(2*d+1)!=0){
      answer=answer+1;
    }
    System.out.println(answer);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    
    int answer = 0;
    
    answer = n/(2*d+1);
    if(n%(2*d+1)!=0){
      answer=answer+1;
    }
    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 answer = 0; answer 0 answer = n/(2*d+1) answer n/(2*d+1) n (2*d+1) 2*d 2 d 1 if(n%(2*d+1)!=0){
      answer=answer+1;
    } n%(2*d+1)!=0 n%(2*d+1) n (2*d+1) 2*d 2 d 1 0 {
      answer=answer+1;
    } answer=answer+1 answer answer+1 answer 1 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 answer = 0;
    
    answer = n/(2*d+1);
    if(n%(2*d+1)!=0){
      answer=answer+1;
    }
    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 answer = 0;
    
    answer = n/(2*d+1);
    if(n%(2*d+1)!=0){
      answer=answer+1;
    }
    System.out.println(answer);
  }
  

  
} Main
import 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 answer = 0;
    
    answer = n/(2*d+1);
    if(n%(2*d+1)!=0){
      answer=answer+1;
    }
    System.out.println(answer);
  }
  

  
}