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=0;
      int left=n;

      for(int i=0;i<n;i++){
        left = left - (1 + 2*d);
        ans++;
        if(left<=0){
          break;
        }
      }

      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=0;
      int left=n;

      for(int i=0;i<n;i++){
        left = left - (1 + 2*d);
        ans++;
        if(left<=0){
          break;
        }
      }

      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=0;
      int left=n;

      for(int i=0;i<n;i++){
        left = left - (1 + 2*d);
        ans++;
        if(left<=0){
          break;
        }
      }

      System.out.println(ans);

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

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

      int ans=0;
      int left=n;

      for(int i=0;i<n;i++){
        left = left - (1 + 2*d);
        ans++;
        if(left<=0){
          break;
        }
      }

      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=0; ans 0 int left=n; left n for(int i=0;i<n;i++){
        left = left - (1 + 2*d);
        ans++;
        if(left<=0){
          break;
        }
      } int i=0; int i=0; i 0 i<n i n i++ i++ i {
        left = left - (1 + 2*d);
        ans++;
        if(left<=0){
          break;
        }
      } {
        left = left - (1 + 2*d);
        ans++;
        if(left<=0){
          break;
        }
      } left = left - (1 + 2*d) left left - (1 + 2*d) left (1 + 2*d) 1 2*d 2 d ans++ ans if(left<=0){
          break;
        } left<=0 left 0 {
          break;
        } break; 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=0;
      int left=n;

      for(int i=0;i<n;i++){
        left = left - (1 + 2*d);
        ans++;
        if(left<=0){
          break;
        }
      }

      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=0;
      int left=n;

      for(int i=0;i<n;i++){
        left = left - (1 + 2*d);
        ans++;
        if(left<=0){
          break;
        }
      }

      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=0;
      int left=n;

      for(int i=0;i<n;i++){
        left = left - (1 + 2*d);
        ans++;
        if(left<=0){
          break;
        }
      }

      System.out.println(ans);

    }
}
