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

[EX Q]: AuSFmN, crSFXM
[EX A]: SF

[EX Q]: apGMPThLTCw, LvMPThYW
[EX A]: MPTh

[EX Q]: OrGCEFupgwu, NvTAEFupNkZ
[EX A]:
EFup