If Dr. Fine Rolo can't put it into English I'm not going to presume to, but for those of you who can't read kanji, it says がんばれ ("ganbare"), which is a command form of がんばる ("ganbaru"). edict says:
頑張る 【がんばる】 (v5r,vi) to persist; to insist on; to stand firm; to try one's best; (P)