instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
YWNPkA, LuNPnN
answer:
NP


question:
zBxuZfJgYrlRSzkmAktO, YNMgYrlRSzklmBOH
answer:
gYrlRSzk


question:
sZshXzAxyKjrQctS, vVCXzAxyKqRqKpx
answer:

XzAxyK