n = gets.chomp.to_i
v = gets.chomp.split.map(&:to_i)

ary = []

n.times do |i|
  ary.push(v[i])
end
arysort = ary.sort

(n-1).times do |i|
  sorezore_wa = (arysort[0] + arysort[1]).quo(2).to_f
  arysort.unshift(sorezore_wa)

  arysort.delete_at(1)
  arysort.delete_at(1)
end

p arysort[0]
