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

Example Input: DQBpdnwVDcnCDEWpD, gAtCdnwVDcnCYv
Example Output: dnwVDcnC

Example Input: YRLHFm, odLHCI
Example Output: LH

Example Input: ZxqqiMzpYNLs, TkeiMzpLTdi
Example Output:
iMzp