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

rCFrfkmXbSHK, mztfkmXwez
fkmX

RNYHvcNnbsUdJLvS, PpNnbsUdglWhl
NnbsUd

ROMMMaUTTLj, eTqMMaURbm

MMaU