lines = []
while line = gets
    lines << line.chomp.split(' ').map(&:to_i)
end

N = lines[0][0]
ingredients = lines[1].sort

pre_ans = ingredients[0].to_f
for i in 2..N do
  pre_ans += ingredients[i-1].to_f * (2 ** (i-2))
end

print pre_ans / (2 ** (N-1))