N = gets.to_i
xs = gets.split.map(&:to_i).sort
diff = xs[1] - xs[0]
(0..N-2).each do |i|
  if xs[i+1] - xs[i] != diff || xs[i+1] - xs[i] == 0
    puts 'NO'
    exit
  end
end
puts 'YES'