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

Example Input: dlzequypR, Puequqv
Example Output: equ

Example Input: vMYfFo, EHYfnP
Example Output: Yf

Example Input: tGmsjOYayjiSnYkMDsIJCMlexE, bixcAGnvSwiSnYkMDsIJqKfFSsIh
Example Output:
iSnYkMDsIJ