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

[EX Q]: EPUxsZtt, KgxsZuXM
[EX A]: xsZ

[EX Q]: IKrQfT, crrQRg
[EX A]: rQ

[EX Q]: XLaXrpgxhmqMzx, dEWdOSrpgxhmUczOiT
[EX A]:
rpgxhm