Listen to 四当五落 四当五落 よんとうごらく sleep four hours and pass, sleep five hours and fail (when cramming for university entrance exams)
Listen to 四大奇書 四大奇書 しだいきしょ Four Classic Novels of Chinese literature (Romance of the Three Kingdoms, Journey to the West, Water Margin, and The Plum in the Golden Vase)