instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
EPUxsZtt, KgxsZuXM
answer:
xsZ


question:
RtAchtNymcswVk, FWRuRchtNymcswUkoERHyML
answer:
chtNymcsw


question:
pySBCdpe, AEBCdOR
answer:

BCd