In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.

[EX Q]: CUxfOt, dyxfNp
[EX A]: xf

[EX Q]: NUuLSmDjCKcJPc, lGGSLIDjCKcJBo
[EX A]: DjCKcJ

[EX Q]: KWBmcY, wuBmfB
[EX A]:
Bm