n = gets.to_i
vv = gets.split.map(&:to_i).sort

made_arr = []

target = vv.shift
target2 = vv.shift
while(true) do
  made_arr << 1.000000 * (target + target2)/ 2

  break if made_arr.size + vv.size == 1
  made_arr.sort!

  if made_arr.size==0
    target = vv.shift
    target2 = vv.shift
    next
  elsif vv.size==0
    target = made_arr.shift
    target2 = made_arr.shift
    next
  end

  if made_arr.first < vv.first
    target = made_arr.shift
    if made_arr.size==0
      target2 = vv.shift
    elsif vv.size==0
      target2 = made_arr.shift
    elsif made_arr.first < vv.first
      target2 = made_arr.shift
    else
      target2 = vv.shift
    end
  else
    target = vv.shift
    if made_arr.size==0
      target2 = vv.shift
    elsif vv.size==0
      target2 = made_arr.shift
    elsif made_arr.first < vv.first
      target2 = made_arr.shift
    else
      target2 = vv.shift
    end
  end
end

puts made_arr.first
