instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
KvPFobZEGs, eKFobZEtnm
answer:
FobZE


question:
NNpkdhvgT, BMkAkdhvrwV
answer:
kdhv


question:
XEvxzelZaWRO, zXIelZaWBUn
answer:

elZaW