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

[EX Q]: gTjTwC, OUjTgM
[EX A]: jT

[EX Q]: sUdaWtsiRgqAYHykrHwjyDvZgD, MJdFXYiRgqAYHykrakSGHMr
[EX A]: iRgqAYHykr

[EX Q]: bEkQJC, URkQZC
[EX A]:
kQ