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

[EX Q]: GlAYDsKQoXy, IxDsKQuK
[EX A]: DsKQ

[EX Q]: vhZuXCsIkQR, YflCuXCsIkLu
[EX A]: uXCsIk

[EX Q]: JZivaArJHs, tzhbiivaArsVc
[EX A]:
ivaAr