定一行个数得出几行#

num：一排定多少个
得出的结论是目前多少排

推演：
count   num     结论
0       3   (2/3) = 0

1       3   (3/3) = 1
2       3   (4/3) = 1
3       3   (5/3) = 1

4       3   (6/3) = 2
5       3   (7/3) = 2
6       3   (8/3) = 2

7       3   (9/3) = 3
8       3   (10/3) = 3
9       3   (11/3) = 3

结论：
row = (count + (num - 1)) / num