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

Example Input: OXdSmcKG, XbDdSmJl
Example Output: dSm

Example Input: JzbEpAquDJFKcNvEWZxVqRV, PFiJlpAquDJFKcNcqOpMeAv
Example Output: pAquDJFKcN

Example Input: wATkafWjxhDU, BYqafWjIEH
Example Output:
afWj