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

Example Input: GrvtMjEvRlmN, ifGOWMjEvRPSOZK
Example Output: MjEvR

Example Input: trHTzJpm, aCHTzVVA
Example Output: HTz

Example Input: KnVZBlRP, oXBZBlGk
Example Output:
ZBl

