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

Example Input: HiGmCdXrmFRJYWLvZbpU, IxhkrmFRJYWLvZLaqRVxPkL
Example Output: rmFRJYWLvZ

Example Input: SODsrWUjUBSgA, WIWUjUBCUUs
Example Output: WUjUB

Example Input: ZlytMkCTTIFrvI, wrzMkCTTIfN
Example Output:
MkCTTI