class Yukicoder
  def initialize
    b = gets.to_i
    n = gets.to_i
    c = []

    n.times do
      c << gets.to_i
    end

    answer = 0

    loop do
      c = c.sort.reverse
      a = c.inject(:+)/2
      max_val = c.max
      b = c.inject(0){|sum, n| sum += (max_val-n)}

      if a < b
        d = c.find{|i| i < max_val}
        c[0] = d
        answer += (max_val-d)
      else
        answer += b
        break
      end
    end

    puts answer
  end
end

Yukicoder.new