instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
hRVyvwHqnN, geHeyvwHqiBiYJ
answer:
yvwHq


question:
AxRSlkQfWHrdlgQG, iXIOrmlkQfWHTy
answer:
lkQfWH


question:
QHXCVXGb, BBCVXrY
answer:

CVX