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

[EX Q]: CkZOSZevST, bbZOSZIg
[EX A]: ZOSZ

[EX Q]: DFRoMPNDAzNgtLsEPseOzC, qykyPjDAzNgtLsEPYTsNrJaNK
[EX A]: DAzNgtLsEP

[EX Q]: fKBaeamDmHFlaa, WQamDmHFljmag
[EX A]:
amDmHFl