instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
LJJvLTK, jpFJvLqh
answer:
JvL


question:
sJRFPufsaWXNeu, AePufsafc
answer:
Pufsa


question:
MJQETeUWOubdnc, EwxMLQETeUWOJeDsfQj
answer:

QETeUWO