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

[EX Q]: cZSEmdgP, YsSEmEIM
[EX A]: SEm

[EX Q]: hVQJkZyKfPoOQEukfAbXDpB, qpojyxWkZyKfPoOQEZkUI
[EX A]: kZyKfPoOQE

[EX Q]: cUJALvpDkpmdkkGbidMNM, BayHQlpDkpmdkkGllCW
[EX A]:
pDkpmdkkG