Problem:
Score : 300 points

Problem Statement

You have a pot and N ingredients. Each ingredient has a real number parameter called value, and the value of the i-th ingredient (1 \leq i \leq N) is v_i.

When you put two ingredients in the pot, they will vanish and result in the formation of a new ingredient. The value of the new ingredient will be (x + y) / 2 where x and y are the values of the ingredients consumed, and you can put this ingredient again in the pot.

After you compose ingredients in this way N-1 times, you will end up with one ingredient. Find the maximum possible value of this ingredient.

Constraints

2 \leq N \leq 50

1 \leq v_i \leq 1000

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
v_1 v_2 \ldots v_N

Output

Print a decimal number (or an integer) representing the maximum possible value of the last ingredient remaining.

Your output will be judged correct when its absolute or relative error from the judge's output is at most 10^{-5}.

Sample Input 1

2
3 4

Sample Output 1

3.5

If you start with two ingredients, the only choice is to put both of them in the pot. The value of the ingredient resulting from the ingredients of values 3 and 4 is (3 + 4) / 2 = 3.5.

Printing 3.50001, 3.49999, and so on will also be accepted.

Sample Input 2

3
500 300 200

Sample Output 2

375

You start with three ingredients this time, and you can choose what to use in the first composition. There are three possible choices:

Use the ingredients of values 500 and 300 to produce an ingredient of value (500 + 300) / 2 = 400. The next composition will use this ingredient and the ingredient of value 200, resulting in an ingredient of value (400 + 200) / 2 = 300.

Use the ingredients of values 500 and 200 to produce an ingredient of value (500 + 200) / 2 = 350. The next composition will use this ingredient and the ingredient of value 300, resulting in an ingredient of value (350 + 300) / 2 = 325.

Use the ingredients of values 300 and 200 to produce an ingredient of value (300 + 200) / 2 = 250. The next composition will use this ingredient and the ingredient of value 500, resulting in an ingredient of value (250 + 500) / 2 = 375.

Thus, the maximum possible value of the last ingredient remaining is 375.

Printing 375.0 and so on will also be accepted.

Sample Input 3

5
138 138 138 138 138

Sample Output 3

138

Solution in Ruby (2.3.3) (judge verdict: Accepted)

# https://atcoder.jp/contests/abc138/tasks/abc138_c

class PriorityQueue
  def initialize(values = [])
    @data = []
    values.each{|value| add(value)}
  end

  def add(value)
    @data.push(value)
    bottom_up
  end

  def peek
    @data[0]
  end

  def poll
    if size == 0
      nil
    elsif size == 1
      @data.pop
    else
      min = @data[0]
      @data[0] = @data.pop # 末尾を先頭へ
      top_down # Queueを再構築
      min
    end
  end

  def size
    @data.size
  end

  private

  def swap(i, j)
    @data[i], @data[j] = @data[j], @data[i]
  end


  def bottom_up
    idx = size - 1
    while has_parent?(idx)
      parent_idx = parent_idx(idx)
      if @data[parent_idx] > @data[idx]
        swap(parent_idx, idx)
        idx = parent_idx
      else
        return
      end
    end
  end

  def top_down
    idx = 0
    while has_child?(idx)
      a = left_child_idx(idx)
      b = right_child_idx(idx)
      if @data[b].nil?
        c = a
      else
        c = @data[a] <= @data[b] ? a : b
      end
      if @data[idx] > @data[c]
        swap(idx, c)
        idx = c
      else
        return
      end
    end
  end

  def parent_idx(idx)
    (idx - (idx.even? ? 2 : 1)) / 2
  end

  def left_child_idx(idx)
    (idx * 2) + 1
  end

  def right_child_idx(idx)
    (idx * 2) + 2
  end

  def has_child?(idx)
    ((idx * 2) + 1) < @data.size
  end

  def has_parent?(idx)
    idx > 0
  end
end


N = gets.to_i
vs = gets.split.map(&:to_i)

queue = PriorityQueue.new(vs)

while queue.size > 1
  ave = (queue.poll + queue.poll) / 2.0
  queue.add(ave)
end

puts queue.poll