[youku for Chinese]

▼ Performance(연출)

https://v.youku.com/v_show/id_XNDQ2MzQ0MDkyMA==.html?spm=a2h3j.8428770.3416059.1

▼ Explanation(해법)

https://v.youku.com/v_show/id_XNDQ2MzQzNjY2NA==.html?spm=a2h3j.8428770.3416059.1