instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
CxwZWv, mkwZgM
answer:
wZ


question:
iUtNuU, iKtNWk
answer:
tN


question:
lvoXZsaUHeA, iXOrZsaUHhicSQ
answer:

ZsaUH