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

Ex Input:
XWKEpwGRkfCFZGOyZQOoypx, lhQkmVqeRkfCFZGOyugPLqs

Ex Output:
RkfCFZGOy


Ex Input:
TdvkBvVyJcSdYGGPfnyml, rIvIvVyJcSdYhtxG

Ex Output:
vVyJcSdY


Ex Input:
taFNtEkzZBfUHjiVi, GgLkzZBfUHjdw

Ex Output:

kzZBfUHj