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();
    int d_new = 2 * d + 1;

    for(int i = 1;; i++) {
      if(i * d_new >= n) {
        System.out.println(i);
        break;
      }
    }

  }

} 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();
    int d_new = 2 * d + 1;

    for(int i = 1;; i++) {
      if(i * d_new >= n) {
        System.out.println(i);
        break;
      }
    }

  }

} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int d_new = 2 * d + 1;

    for(int i = 1;; i++) {
      if(i * d_new >= n) {
        System.out.println(i);
        break;
      }
    }

  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int d_new = 2 * d + 1;

    for(int i = 1;; i++) {
      if(i * d_new >= n) {
        System.out.println(i);
        break;
      }
    }

  } 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 int d_new = 2 * d + 1; d_new 2 * d + 1 2 * d 2 d 1 for(int i = 1;; i++) {
      if(i * d_new >= n) {
        System.out.println(i);
        break;
      }
    } int i = 1; int i = 1; i 1 i++ i++ i {
      if(i * d_new >= n) {
        System.out.println(i);
        break;
      }
    } {
      if(i * d_new >= n) {
        System.out.println(i);
        break;
      }
    } if(i * d_new >= n) {
        System.out.println(i);
        break;
      } i * d_new >= n i * d_new i d_new n {
        System.out.println(i);
        break;
      } System.out.println(i) System.out.println System.out System System.out i break; 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();
    int d_new = 2 * d + 1;

    for(int i = 1;; i++) {
      if(i * d_new >= n) {
        System.out.println(i);
        break;
      }
    }

  }

} public class Main {

  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int d = sc.nextInt();
    int d_new = 2 * d + 1;

    for(int i = 1;; i++) {
      if(i * d_new >= n) {
        System.out.println(i);
        break;
      }
    }

  }

} 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();
    int d_new = 2 * d + 1;

    for(int i = 1;; i++) {
      if(i * d_new >= n) {
        System.out.println(i);
        break;
      }
    }

  }

}
