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

Example Input: WFAPUCgVYbmZiFlacUzyv, xQFiekrgPUCgVYbmZUEtl
Example Output: PUCgVYbmZ

Example Input: CdRbREFMEDTXnEzgn, zHLEMMEDTXnEPH
Example Output: MEDTXnE

Example Input: gsXjOJqcRIrH, LoLICOJqcRdkH
Example Output:
OJqcR