instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
HKCoXQsLRtowYJ, PGRzNUQsLRtoLcqkn
answer:
QsLRto

question:
bdCOjNchdKtvWzOI, FwejNchdKhEd
answer:
jNchdK

question:
ZQMQHxN, ZmdMQHpx
answer:
MQH