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

[EX Q]: QqtCFzXHPNFXx, XECFzXHPSGwUuk
[EX A]: CFzXHP

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

[EX Q]: lsNwypFwhKP, diEfLwypFwEKqCN
[EX A]:
wypFw