import java.util.*;

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

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