n = gets.to_i
kamo = gets.chomp.split.map(&:to_i)
kamo = kamo.sort.reverse
diff = 0

if kamo.uniq.length != n
    puts "NO"
else
    diff = kamo[0] - kamo[1]
    for i in 1..n-2
        if diff != (kamo[i] - kamo[i+1])
            puts "NO"
            return
        end
    end
    puts "YES"
end