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

Example Input: YRLHFm, odLHCI
Example Output: LH

Example Input: DhhYhrqVMXSoyvXQwqPKzWARAP, CaMXSoyvXQwqcDDtMsVqD
Example Output: MXSoyvXQwq

Example Input: iXFvzUWjdC, AeuFvzUcqc
Example Output:
FvzU