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

Example Input: BmxgSFWBlVX, kGgKrgSFWBlGunFcZ
Example Output: gSFWBl

Example Input: pySBCdpe, AEBCdOR
Example Output: BCd

Example Input: PFaeWWiCFPBjqPXjGbSOiucGKI, UdMkQPBjqPXjGbLsGdvMRbJ
Example Output:
PBjqPXjGb