instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
QlJnxO, BLJnCQ
answer:
Jn


question:
NxgzLSzFGa, JvLzLSzsuj
answer:
zLSz


question:
gqOoZvxHYfd, zFIdZvxHSqO
answer:

ZvxH