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

Ex Input:
IGHhMfqLeBpnullsPInfBH, LTDBpnullsPIBynwCrCQ

Ex Output:
BpnullsPI

Ex Input:
spUbdWDLWCeqr, vIuHkWDLWCQEPaz

Ex Output:
WDLWC

Ex Input:
ziJtPJJDoOTyZUtqxR, xGdDoOTyZUrvuvgS

Ex Output:
DoOTyZU