Heavenly stems and earthly branches, referred to as "dry branch". In the ancient calendar of China, A, B, C, D, E, Ji, G, Xin, Ren and Gui were called "ten heavenly stems", while Zi, Ugly, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai were called "twelve earthly branches". Ten branches and twelve branches are matched in turn to form sixty basic units, and they cooperate with each other in a fixed order to form branches and branches.

This problem is actually to find the least common multiple of 10 and 12.