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

[EX Q]: PQSFjlnU, kTSFjMUh
[EX A]: SFj

[EX Q]: aWshKwEuYBBdSwIAyXw, wfVuYBBdSwIAseTxR
[EX A]: uYBBdSwIA

[EX Q]: pyGPZbaIoy, ElZbaIZIl
[EX A]:
ZbaI