N = gets.chomp.to_i
num_arr = gets.chomp.split(" ").map(&:to_i).sort
initial = (num_arr[0] + num_arr[1])/2.to_f
num = 0

num_arr.sort.each_with_index do |n, i|
  next if i == 0 || i == 1
  if i == 2
    num = (num_arr[i] + initial)/2.to_f
  else
    num = (num_arr[i] + num)/2.to_f
  end
end

if N == 2
  puts initial
else
  puts num
end