N, X = gets.split.map(&:to_i)
S = gets.split.map(&:to_i)
A = S.map { |s| X - s }
B = S.map { |s| X - Rational(s, 2) }

a_sum = A.sum

A.zip(B) do |a, b|
  x = a_sum - a

  if x + b == X
    puts x
    exit
  end
end