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

Example Input: BfCCzPNLBbwCoxMVAG, vhwNLBbwCbH
Example Output: NLBbwC

Example Input: nxoXDohHr, WcbkXDohFbJ
Example Output: XDoh

Example Input: CssuvIkuslte, RIYHvIkusAne
Example Output:
vIkus