N = gets.split('\n').map(&:to_i)
nums = gets.chomp.split(' ').map(&:to_f).sort
n = N[0].to_i
for i in 1..n-2 do 
  a = (nums[0] + nums[1])/2
  nums.delete_at(0)
  nums.delete_at(0)
  nums << a
  nums.sort
end

ans = (nums[0] + nums[1])/2

puts ans