_ = gets.to_i
items = gets.chomp.split(' ').map(&:to_f)
def pick(items)
  current = 1001
  result = [0, 0]
  items.each_index do |i|
    v1 = items[i]
    (i + 1).upto(items.count - 1) do |j|
      v2 = items[j]
      tmp = (v1 - v2).abs
      if current > tmp
        result = [i, j]
        current = tmp
      end
    end
  end
  result
end
while items.count > 1
  picked = pick(items)
  new_item = (items[picked[0]] + items[picked[1]]) / 2.0
  items.delete_at(picked[1])
  items.delete_at(picked[0])
  items.push(new_item)
end
puts items[0]