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:
kyADtWLlnmYv, tcaKvDtWLlnvBq
answer:
DtWLln


question:
lLRTMluqaTQ, lLCDTMluqdtw
answer:

TMluq