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

vs.sort!

numerator = vs[0] + vs[1]
denominator = 2

vs[2..-1].each do |v|
  numerator += v * denominator
  denominator *= 2
  gcd = numerator.gcd(denominator)
  numerator /= gcd
  denominator /= gcd
end

puts numerator / denominator.to_f

