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

Ex Input:
ktABEFESAVHZkkY, uMjxiESAVHZkZgWUte

Ex Output:
ESAVHZk

Ex Input:
ZhHtTXaUmsQfUMNrnt, KvvebSXaUmsQfBspwM

Ex Output:
XaUmsQf

Ex Input:
JuXDGUpT, veXDGUEMaf

Ex Output:
XDGU