def priority_push(array:, num:)
  index = array.bsearch_index { |i| i > num}
  if index.nil?
    array.push(num)
  else
    array.insert(index, num)
  end
end

N = gets.to_i
arr = gets.split.map(&:to_i)
arr = arr.sort

while arr.count > 1
  a = arr.shift
  b = arr.shift
  output a, b, arr
  priority_push(array: arr, num: Rational(a + b, 2))
end

puts arr[0].to_f