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

Example Input: YHLJZrFQ, aSLJZQuo
Example Output: LJZ

Example Input: krnkpodgfpCKtfCqyzUbymWbxi, DydgSWpCKtfCqyzDaMsjqc
Example Output: pCKtfCqyz

Example Input: uoEoNQPgBuWd, BRNQPgBqTV
Example Output:
NQPgB