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

[EX Q]: rEHxRBOktYreNkK, NCOktYreFFCFwi
[EX A]: OktYre

[EX Q]: OgWFOfjNYmXVjBBvOdunIc, eGljKGnzFKFOfjNYmXVjdlqsT
[EX A]: FOfjNYmXVj

[EX Q]: SmqYTVfvMdCtMlSr, diABEfvMdCtPao
[EX A]:
fvMdCt