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

Ex Input:
UCbReSfuLcbzmBCl, snQRReSfuLcbzmjqVPSdpp

Ex Output:
ReSfuLcbzm

Ex Input:
qQkmYsYN, UhkmYHSy

Ex Output:
kmY

Ex Input:
WIdIxjBEnyxzzZTt, oxyxjBEnyxNTdCa

Ex Output:
xjBEnyx