instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
QqtCFzXHPNFXx, XECFzXHPSGwUuk
answer:
CFzXHP


question:
BmwpAnWJ, klVwpAFw
answer:
wpA


question:
gaVgOGBvvPSHxbZBcBYLFo, zqRwVBvvPSHxbZCfxX
answer:

BvvPSHxbZ


