import java.util.Scanner;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    double N = Integer.parseInt(sc.next());
    double D = Integer.parseInt(sc.next());
    System.out.println((int)Math.ceil(N/(2*D+1)));
  }
} import java.util.Scanner; Scanner java.util public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    double N = Integer.parseInt(sc.next());
    double D = Integer.parseInt(sc.next());
    System.out.println((int)Math.ceil(N/(2*D+1)));
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    double N = Integer.parseInt(sc.next());
    double D = Integer.parseInt(sc.next());
    System.out.println((int)Math.ceil(N/(2*D+1)));
  } main {
    Scanner sc = new Scanner(System.in);
    double N = Integer.parseInt(sc.next());
    double D = Integer.parseInt(sc.next());
    System.out.println((int)Math.ceil(N/(2*D+1)));
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double N = Integer.parseInt(sc.next()); N Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc double D = Integer.parseInt(sc.next()); D Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next 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 = Integer.parseInt(sc.next());
    double D = Integer.parseInt(sc.next());
    System.out.println((int)Math.ceil(N/(2*D+1)));
  }
} public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    double N = Integer.parseInt(sc.next());
    double D = Integer.parseInt(sc.next());
    System.out.println((int)Math.ceil(N/(2*D+1)));
  }
} Main
import java.util.Scanner;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    double N = Integer.parseInt(sc.next());
    double D = Integer.parseInt(sc.next());
    System.out.println((int)Math.ceil(N/(2*D+1)));
  }
}
