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

ZRjPgqbLL, uIsmPgqbBB
Pgqb

nWTnWqkLqYTBxT, cSTnWqkLqYwXmxRF
TnWqkLqY

KnVZBlRP, oXBZBlGk

ZBl