n = gets.chomp.split(" ").map(&:to_i)[0]

values = gets.chomp.split(" ").map(&:to_f).sort

while values.length > 1 do
    mixed_v = (values[0] + values[1]).to_f / 2
    values.shift(2)
    if values.empty?
        values = [mixed_v]
        break
    end
    values.each_with_index do |v, i|
        if mixed_v < v
            values.insert(i, mixed_v)
            break
        end
    end
end

p values[0]
