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

Example Input: CxwZWv, mkwZgM
Example Output: wZ

Example Input: xeKSiBafhOWBbYwlGaQ, GUfIsKgafhOWBbYiFWnptAt
Example Output: afhOWBbY

Example Input: TsvSpDiXxthIDCxv, mIaOYXxthIDCqdoBqP
Example Output:
XxthIDC