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

Example Input: aWshKwEuYBBdSwIAyXw, wfVuYBBdSwIAseTxR
Example Output: uYBBdSwIA

Example Input: QEEVsnbQIgrxaZmflaZ, dPSbljkdQIgrxaZmgVzMT
Example Output: QIgrxaZm

Example Input: xtCJGe, DXCJSw
Example Output:
CJ