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

Example Input: QqtCFzXHPNFXx, XECFzXHPSGwUuk
Example Output: CFzXHP

Example Input: uGDJixAmSiVaFRmfKRM, NsTGxsJixAmSiVageSw
Example Output: JixAmSiVa

Example Input: NfAwuoKUeWU, OhAwuoKGmeTi
Example Output:
AwuoK