n = gets.to_i
nums = gets.split.map &:to_f
c = 0
(n-1).times do 
    a = nums.min
    nums.delete_at(nums.index(a))
    b = nums.min
    nums.delete_at(nums.index(b))
    
    c = (a+b)/2
    nums.push(c)
end

puts c