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]: QgkpBHsrfRYJCa, AdjbKLpBHsrfbpBC
[EX A]: pBHsrf

[EX Q]: iSFTnY, sHFTYE
[EX A]:
FT