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

Example Input: CdRbREFMEDTXnEzgn, zHLEMMEDTXnEPH
Example Output: MEDTXnE

Example Input: AxRSlkQfWHrdlgQG, iXIOrmlkQfWHTy
Example Output: lkQfWH

Example Input: FpbxdMTJeQDXNSQowpX, QvuIJeQDXNSEgmTwnB
Example Output:
JeQDXNS