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