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

Example Input: ocjsZZfSBBopDtgWUT, rWmgzsZZfSBBoGWQ
Example Output: sZZfSBBo

Example Input: STvKOHq, XMGvKOdyM
Example Output: vKO

Example Input: tgbqdoI, nwbqdnAx
Example Output:
bqd