instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
XeQwOS, OuQwNR
answer:
Qw


question:
DFRoMPNDAzNgtLsEPseOzC, qykyPjDAzNgtLsEPYTsNrJaNK
answer:
DAzNgtLsEP


question:
vytthSjj, XVttthSFAvk
answer:

tthS