[youku for Chinese]
▼ Performance(연출)
https://v.youku.com/v_show/id_XNDQwMTg3NDU4MA==.html?spm=a2h3j.8428770.3416059.1
▼ Explanation(해법)

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