instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
CiTNsbepy, DFNsbeZl
answer:
Nsbe


question:
UtUSmsOI, dCUSmGoQ
answer:
USm


question:
xLWkGOjKsILiZc, NQOjKsIxZz
answer:

OjKsI