num = gets.to_i
list = gets.split(" ").map(&:to_i).sort
a = list[0] - list[1]
for i in 2..num-1
    if list[i] - list[i+1] != a || list[i] - list[i+1] == 0
        puts "NO"
        break
    end
    if i == num-1
        puts "YES"
        break
    end
end