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();
    sc.close();

    double r = (double) N / (2 * D + 1);

    int res = (int) Math.ceil(r);

    System.out.println(res);

  }
  
} 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();
    sc.close();

    double r = (double) N / (2 * D + 1);

    int res = (int) Math.ceil(r);

    System.out.println(res);

  }
  
} Main public static void main (String[] args) {

    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int D = sc.nextInt();
    sc.close();

    double r = (double) N / (2 * D + 1);

    int res = (int) Math.ceil(r);

    System.out.println(res);

  } main {

    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int D = sc.nextInt();
    sc.close();

    double r = (double) N / (2 * D + 1);

    int res = (int) Math.ceil(r);

    System.out.println(res);

  } 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 sc.close() sc.close sc double r = (double) N / (2 * D + 1); r (double) N / (2 * D + 1) (double) N (2 * D + 1) 2 * D 2 D 1 int res = (int) Math.ceil(r); res (int) Math.ceil(r) Math.ceil Math r System.out.println(res) System.out.println System.out System System.out res 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();
    sc.close();

    double r = (double) N / (2 * D + 1);

    int res = (int) Math.ceil(r);

    System.out.println(res);

  }
  
} public class Main {

  public static void main (String[] args) {

    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int D = sc.nextInt();
    sc.close();

    double r = (double) N / (2 * D + 1);

    int res = (int) Math.ceil(r);

    System.out.println(res);

  }
  
} 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();
    sc.close();

    double r = (double) N / (2 * D + 1);

    int res = (int) Math.ceil(r);

    System.out.println(res);

  }
  
}