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

[EX Q]: lMRuEThD, wqQRuEKp
[EX A]: RuE

[EX Q]: vMsEJRoLkWcmkuwNRz, ZmoLkWcmVZiBv
[EX A]: oLkWcm

[EX Q]: sgpseLanxhKiPafywL, QsAEmfeLanxhKiKFJtSDMR
[EX A]:
eLanxhKi