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: sdGIVJPsWWszKPCGk, ghRJPsWWszKcJUg
Example Output: JPsWWszK

Example Input: WqTRCD, PLTRGo
Example Output:
TR