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 ans;

    if(n % (2 * d + 1) == 0){
      ans = n / (2 * d + 1);
    } else {
      ans = (n / (2 * d + 1)) + 1;
    }

    System.out.println(ans);
  }
} 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 ans;

    if(n % (2 * d + 1) == 0){
      ans = n / (2 * d + 1);
    } else {
      ans = (n / (2 * d + 1)) + 1;
    }

    System.out.println(ans);
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int ans;

    if(n % (2 * d + 1) == 0){
      ans = n / (2 * d + 1);
    } else {
      ans = (n / (2 * d + 1)) + 1;
    }

    System.out.println(ans);
  } main {
    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int ans;

    if(n % (2 * d + 1) == 0){
      ans = n / (2 * d + 1);
    } else {
      ans = (n / (2 * d + 1)) + 1;
    }

    System.out.println(ans);
  } 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 ans; ans if(n % (2 * d + 1) == 0){
      ans = n / (2 * d + 1);
    } else {
      ans = (n / (2 * d + 1)) + 1;
    } n % (2 * d + 1) == 0 n % (2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 0 {
      ans = n / (2 * d + 1);
    } ans = n / (2 * d + 1) ans n / (2 * d + 1) n (2 * d + 1) 2 * d 2 d 1 {
      ans = (n / (2 * d + 1)) + 1;
    } ans = (n / (2 * d + 1)) + 1 ans (n / (2 * d + 1)) + 1 (n / (2 * d + 1)) n (2 * d + 1) 2 * d 2 d 1 1 System.out.println(ans) System.out.println System.out System System.out ans 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 ans;

    if(n % (2 * d + 1) == 0){
      ans = n / (2 * d + 1);
    } else {
      ans = (n / (2 * d + 1)) + 1;
    }

    System.out.println(ans);
  }
} public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int d = sc.nextInt();
    int ans;

    if(n % (2 * d + 1) == 0){
      ans = n / (2 * d + 1);
    } else {
      ans = (n / (2 * d + 1)) + 1;
    }

    System.out.println(ans);
  }
} 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 ans;

    if(n % (2 * d + 1) == 0){
      ans = n / (2 * d + 1);
    } else {
      ans = (n / (2 * d + 1)) + 1;
    }

    System.out.println(ans);
  }
}
