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

Example Input: GlAYDsKQoXy, IxDsKQuK
Example Output: DsKQ

Example Input: eeoJEtGHPDvHck, ezPGHPDvHSf
Example Output: GHPDvH

Example Input: mbsNJxCD, UzNJxNG
Example Output:
NJx