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

[EX Q]: NmtypJ, tQtyZD
[EX A]: ty

[EX Q]: rCFrfkmXbSHK, mztfkmXwez
[EX A]: fkmX

[EX Q]: pYmzRnGPQVPrqPApKTyvaO, tNGPQVPrqPVTh
[EX A]:
GPQVPrqP