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

Example Input: ZKMRTxCxbsbX, iovHrMRTxCxbsjv
Example Output: MRTxCxbs

Example Input: ocjsZZfSBBopDtgWUT, rWmgzsZZfSBBoGWQ
Example Output: sZZfSBBo

Example Input: fWJdaAfOCfejXZvidHM, gOpfOCfejXZbtLvSLZI
Example Output:
fOCfejXZ