n=gets.chomp!.to_i
as=gets.split(" ").map(&:to_i)
#au=Array.new
as.sort!
if as.length<=2
  p as.inject(:+)/2.0
  exit
end

while as.length>=2
as << (as[0].to_i+as[1].to_i) / 2.0
as.delete_at(0)
as.delete_at(0)
as.sort!
end

p as[0]