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

Example Input: QjDQjzAIsnYgNmmetl, vyqDQjzAIsnNajYEheP
Example Output: DQjzAIsn

Example Input: NxgzLSzFGa, JvLzLSzsuj
Example Output: zLSz

Example Input: iPdoVatHbgcKZyi, kVDkftHbgcKiOddb
Example Output:
tHbgcK