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

Ex Input:
NxgzLSzFGa, JvLzLSzsuj

Ex Output:
zLSz

Ex Input:
NNpkdhvgT, BMkAkdhvrwV

Ex Output:
kdhv

Ex Input:
MaNOsOyFZymjJVOsk, XqhOyFZymdJZtY

Ex Output:
OyFZym