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

[EX Q]: WFAPUCgVYbmZiFlacUzyv, xQFiekrgPUCgVYbmZUEtl
[EX A]: PUCgVYbmZ

[EX Q]: bOvlVNWf, iivlVzWt
[EX A]: vlV

[EX Q]: tMybAEkgBLsuJkagsbDlEEuK, kPOVjrkBLsuJkagshLdg
[EX A]:
BLsuJkags