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]: fBpRXPkikQokGVeS, FwUbKXkikQokGos
[EX A]: kikQokG

[EX Q]: fVYmknIFxnZTftLpXIkce, poWrnTLxnZTftLpQU
[EX A]:
xnZTftLp