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

Ex Input:
QlJnxO, BLJnCQ

Ex Output:
Jn

Ex Input:
zgJGhxLU, EwJGhedW

Ex Output:
JGh

Ex Input:
MjjKLoIsYzIdoJULAO, BMtFlojKLoIsYzzYxd

Ex Output:
jKLoIsYz