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

Example Input: apGMPThLTCw, LvMPThYW
Example Output: MPTh

Example Input: AkYuNemHGBEDF, uluNemHGAycbWX
Example Output: uNemHG

Example Input: RZAxSfKOYDfNOpiaK, JrCHRBfKOYDfNOpexDg
Example Output:
fKOYDfNOp