count = gets.chomp.to_i
list = gets.split.map(&:to_i).sort
flag = list[1] - list[0]
for i in 1...list.size - 1 do 
	distance = list[i + 1] - list[i]
	if flag != distance
		flag = 0
		break
	end
end
puts flag == 0 ? "NO" : "YES"