N, M = gets.split.map(&:to_i)
B = gets.split.map(&:to_i)

ans = N - 1

wp = B.select { |b| B.last <= b + M }
r = Rational(M, wp.size)
val = 0.0

wp.each do |b|
  cnt = B.first + r + (N - b) - 1
  val += cnt
end

puts [ans, Rational(val, wp.size).to_f.round(12)].min