instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
UvYbfKFybXofcwLRrLRiK, BgMZKFybXofcVe
answer:
KFybXofc


question:
VByrCcgcxCfPGDFqIWGloQZTMQf, OqfPGDFqIWGlalTCCkKkMf
answer:
fPGDFqIWGl


question:
WQgfCHhFe, qEMgfCHXk
answer:

gfCH