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

Ex Input:
lQwpMQRxuVbJDv, UkzwpMQRxuDVT

Ex Output:
wpMQRxu

Ex Input:
CzkPtkpMTDeNZwCPbJJn, HzpMVDeNZwCPbJVOU

Ex Output:
DeNZwCPbJ

Ex Input:
OVZxWYzAAxG, rStOxWYzJeoC

Ex Output:
xWYz