import java.util.Scanner;
import java.lang.StringBuilder;
import java.math.BigInteger;

public class Main{
  
  
  
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    double n, d;
    n = sc.nextDouble();
    d = sc.nextDouble();
    
    System.out.println((int)Math.ceil(n/(2*d+1)));
    
    
    
    
    
    
//    System.out.println(time);
    
    
  }
} import java.util.Scanner; Scanner java.util import java.lang.StringBuilder; StringBuilder java.lang import java.math.BigInteger; BigInteger java.math public class Main{
  
  
  
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    double n, d;
    n = sc.nextDouble();
    d = sc.nextDouble();
    
    System.out.println((int)Math.ceil(n/(2*d+1)));
    
    
    
    
    
    
//    System.out.println(time);
    
    
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    double n, d;
    n = sc.nextDouble();
    d = sc.nextDouble();
    
    System.out.println((int)Math.ceil(n/(2*d+1)));
    
    
    
    
    
    
//    System.out.println(time);
    
    
  } main {
    Scanner sc = new Scanner(System.in);
    
    double n, d;
    n = sc.nextDouble();
    d = sc.nextDouble();
    
    System.out.println((int)Math.ceil(n/(2*d+1)));
    
    
    
    
    
    
//    System.out.println(time);
    
    
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double n n d; d n = sc.nextDouble() n sc.nextDouble() sc.nextDouble sc d = sc.nextDouble() d sc.nextDouble() sc.nextDouble sc System.out.println((int)Math.ceil(n/(2*d+1))) System.out.println System.out System System.out (int)Math.ceil(n/(2*d+1)) Math.ceil Math n/(2*d+1) n (2*d+1) 2*d 2 d 1 String[] args args public class Main{
  
  
  
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    double n, d;
    n = sc.nextDouble();
    d = sc.nextDouble();
    
    System.out.println((int)Math.ceil(n/(2*d+1)));
    
    
    
    
    
    
//    System.out.println(time);
    
    
  }
} public class Main{
  
  
  
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    double n, d;
    n = sc.nextDouble();
    d = sc.nextDouble();
    
    System.out.println((int)Math.ceil(n/(2*d+1)));
    
    
    
    
    
    
//    System.out.println(time);
    
    
  }
} Main
import java.util.Scanner;
import java.lang.StringBuilder;
import java.math.BigInteger;

public class Main{
  
  
  
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    double n, d;
    n = sc.nextDouble();
    d = sc.nextDouble();
    
    System.out.println((int)Math.ceil(n/(2*d+1)));
    
    
    
    
    
    
//    System.out.println(time);
    
    
  }
}