import java.util.*;


public class Main {
    public static void main(String[] args) {
      
      Scanner sc = new Scanner(System.in);
      int n = Integer.parseInt(sc.next());
      int d = Integer.parseInt(sc.next());
      int ans = 0;
      int sum = 0;
      for (int i =0; sum < n; i++) {
        sum += d * 2 + 1;
        ans += 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 = Integer.parseInt(sc.next());
      int d = Integer.parseInt(sc.next());
      int ans = 0;
      int sum = 0;
      for (int i =0; sum < n; i++) {
        sum += d * 2 + 1;
        ans += 1;
      }
      System.out.println(ans);
    }
} Main public static void main(String[] args) {
      
      Scanner sc = new Scanner(System.in);
      int n = Integer.parseInt(sc.next());
      int d = Integer.parseInt(sc.next());
      int ans = 0;
      int sum = 0;
      for (int i =0; sum < n; i++) {
        sum += d * 2 + 1;
        ans += 1;
      }
      System.out.println(ans);
    } main {
      
      Scanner sc = new Scanner(System.in);
      int n = Integer.parseInt(sc.next());
      int d = Integer.parseInt(sc.next());
      int ans = 0;
      int sum = 0;
      for (int i =0; sum < n; i++) {
        sum += d * 2 + 1;
        ans += 1;
      }
      System.out.println(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = Integer.parseInt(sc.next()); n Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int d = Integer.parseInt(sc.next()); d Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int ans = 0; ans 0 int sum = 0; sum 0 for (int i =0; sum < n; i++) {
        sum += d * 2 + 1;
        ans += 1;
      } int i =0; int i =0; i 0 sum < n sum n i++ i++ i {
        sum += d * 2 + 1;
        ans += 1;
      } {
        sum += d * 2 + 1;
        ans += 1;
      } sum += d * 2 + 1 sum d * 2 + 1 d * 2 d 2 1 ans += 1 ans 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 = Integer.parseInt(sc.next());
      int d = Integer.parseInt(sc.next());
      int ans = 0;
      int sum = 0;
      for (int i =0; sum < n; i++) {
        sum += d * 2 + 1;
        ans += 1;
      }
      System.out.println(ans);
    }
} public class Main {
    public static void main(String[] args) {
      
      Scanner sc = new Scanner(System.in);
      int n = Integer.parseInt(sc.next());
      int d = Integer.parseInt(sc.next());
      int ans = 0;
      int sum = 0;
      for (int i =0; sum < n; i++) {
        sum += d * 2 + 1;
        ans += 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 = Integer.parseInt(sc.next());
      int d = Integer.parseInt(sc.next());
      int ans = 0;
      int sum = 0;
      for (int i =0; sum < n; i++) {
        sum += d * 2 + 1;
        ans += 1;
      }
      System.out.println(ans);
    }
}