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

Example Input: ktABEFESAVHZkkY, uMjxiESAVHZkZgWUte
Example Output: ESAVHZk

Example Input: HhBhJMpxpty, MxTJMpxnQEf
Example Output: JMpx

Example Input: LBhLwZrHss, iiryLwZrHTZS
Example Output:
LwZrH