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

[EX Q]: rCFrfkmXbSHK, mztfkmXwez
[EX A]: fkmX

[EX Q]: aWshKwEuYBBdSwIAyXw, wfVuYBBdSwIAseTxR
[EX A]: uYBBdSwIA

[EX Q]: yCnkHiqnmwBmvVHvWzSx, vXVnkHiqnmwBmCeuszxvM
[EX A]:
nkHiqnmwBm

