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

Ex Input:
CUxfOt, dyxfNp

Ex Output:
xf


Ex Input:
VutZiVkDQcVpQO, BDQVDyBdiVkDQcVpuvNN

Ex Output:
iVkDQcVp


Ex Input:
XWKEpwGRkfCFZGOyZQOoypx, lhQkmVqeRkfCFZGOyugPLqs

Ex Output:

RkfCFZGOy


