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:
umXfmRnUgALpFAqBaKfNfo, aOAXWnUgALpFAqBmNpTCdj
answer:
nUgALpFAqB


question:
BaKwTnJGBGszlmoTuI, bfsHJGBGszlMJm
answer:

JGBGszl