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

[EX Q]: fVEFJa, WtEFYK
[EX A]: EF

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

[EX Q]: DNvpPLhbRibibOneSszLmknsqv, jibNUIyESRibibOneSswqxnzFAd
[EX A]:
RibibOneSs