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

[EX Q]: tyVlHfTPLRSdFilXnSfqQ, bkTPLRSdFiMgXC
[EX A]: TPLRSdFi

[EX Q]: sRpnJlgECTHh, JXfmNJlgECKyry
[EX A]: JlgEC

[EX Q]: ovaXTf, NgaXZk
[EX A]:
aX