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

Example Input: RNYHvcNnbsUdJLvS, PpNnbsUdglWhl
Example Output: NnbsUd

Example Input: DwLGzwYOWjtzIunE, TTViSbkwYOWjtzNqUOOz
Example Output: wYOWjtz

Example Input: dXNjob, oqNjDn
Example Output:
Nj