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

Example Input: kyADtWLlnmYv, tcaKvDtWLlnvBq
Example Output: DtWLln

Example Input: trHTzJpm, aCHTzVVA
Example Output: HTz

Example Input: aWYsNeABKJsuztmeUvHap, RtsNeABKJsuzhZngnA
Example Output:
sNeABKJsuz