N = gets.chomp.to_i
v = gets.chomp.split(" ").map(&:to_i)
v.sort!
work = 0
for i in 1..N-1 do
    if i == 1
        work = (v[i].to_f + v[i-1].to_f) / 2 
    else
        work = (work.to_f + v[i].to_f) / 2
    end
end
puts work