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

Example Input: xMxyohPBlJIEBqghiMdBQPwq, xsBlJIEBqghlMosK
Example Output: BlJIEBqgh

Example Input: ftvxfhsnJEygzV, JYxSfhsnJnIqkW
Example Output: fhsnJ

Example Input: ROAuYCqpSqATITX, NILxpAuYCqpSkcaooN
Example Output:
AuYCqpS