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

Example Input: lrBJDRkT, jmBJDrI
Example Output: BJD

Example Input: xeKSiBafhOWBbYwlGaQ, GUfIsKgafhOWBbYiFWnptAt
Example Output: afhOWBbY

Example Input: ZhGookkUMzhpyiUopulD, CuyhRDQskUMzhpyiUonubA
Example Output:
kUMzhpyiUo