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

Example Input: trHTzJpm, aCHTzVVA
Example Output: HTz

Example Input: GnElFKBIoYmAdvz, GrElFKBIoMo
Example Output: ElFKBIo

Example Input: DwkTGsIXLfmjMV, VqRlMxtsSBkTGsIXLfmjbvI
Example Output:
kTGsIXLfmj