instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
vytthSjj, XVttthSFAvk
answer:
tthS


question:
BVipiZoGXaWdjmDsxWP, yxppsiYkiZoGXaWdjoDRuKW
answer:
iZoGXaWdj


question:
qTHDtoBcFlTI, VywkwxDtoBcFSLS
answer:

DtoBcF