instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
dReySjyqecU, loSjyqiRl
answer:
Sjyq


question:
PQSFjlnU, kTSFjMUh
answer:
SFj


question:
BWMIdWHdWO, cyCMIdWdoPI
answer:

MIdW