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

Ex Input:
vSFxjd, AHFxpi

Ex Output:
Fx

Ex Input:
xeKSiBafhOWBbYwlGaQ, GUfIsKgafhOWBbYiFWnptAt

Ex Output:
afhOWBbY

Ex Input:
npiwfAffGYnUk, fvAffGYmza

Ex Output:
AffGY