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
i=0
while i <= n
d = (as[0].to_i+as[1].to_i) / 2.0
as[i..i+1] = d
i+=1
  if as.length<=2
    break
  end
end
ans = (as[0]+as[1]) / 2
p ans
