n = gets.to_i
v_array = gets.split(' ').map(&:to_f)

permutation_array = v_array.permutation
result = []
p permutation_array
permutation_array.map do |array|
  tmp = (array[0] + array[1])/2
  (2..(n-1)).each do |i|
    tmp = (tmp + array[i]) / 2
  end
  result << tmp
end

puts result.uniq.max