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

Example Input: biAihydBoNlzR, IAloNhydBolwUz
Example Output: hydBo

Example Input: UCbReSfuLcbzmBCl, snQRReSfuLcbzmjqVPSdpp
Example Output: ReSfuLcbzm

Example Input: QMKuhqMj, FybKuhqfVw
Example Output:
Kuhq