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

Example Input: iYSNsY, HSSNhP
Example Output: SN

Example Input: zfUPUDeKbCMQa, BkAJFJUDeKbCMZmkFu
Example Output: UDeKbCM

Example Input: iMQuyCaTkIHTMuziqju, JLvahqZIkIHTMuzizNrvXBLu
Example Output:
kIHTMuzi