instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
PQCjJwXurLeN, vsjJwXuOy
answer:
jJwXu


question:
atDgsOWuP, UJMgsOrwj
answer:
gsO


question:
HMgBTbFuWRg, LtTbFuWdZC
answer:

TbFuW