n = gets.chomp.to_i
facts = gets.chomp.split(' ').map(&:to_i)

facts.sort!
value = 0
(1..(facts.length - 1)).each do |i|
  if i == 1
    value = ((facts[0] + facts[i])/2).to_f
  else
    value = ((value + facts[i])/2).to_f
  end
end
puts "#{value}"
