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

Example Input: ylyLVUjsmMrXMFAPDGIZsHq, cYymMrXMFAPjm
Example Output: mMrXMFAP

Example Input: AuSFmN, crSFXM
Example Output: SF

Example Input: RMTRbUsFwFCxBO, oMUsFwFaE
Example Output:
UsFwF