Growing Up is the first Korean-language studio album by South Korean singer-songwriter and actress IU. It was released on April 23, 2009, as a follow-up to her 2008 debut mini-album "Lost and Found". Two of the album's 16 tracks, "Boo" and "You Know (있잖아) (Rock Ver.)", were released as singles.
Boo was the second single on the album.
I am assuming the first track listed is the first single.