n = gets.to_i
vs = gets.chomp.split(" ").map(&:to_f)

sorted = vs.sort
result = 0
sorted.each_with_index do |val, i|
    if i == sorted.length - 1
        break
    end
    if i == 0
        result += (val + sorted[i + 1]) / 2
        next
    end
    result = (result + sorted[i + 1]) / 2
end
print result    