instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
EPUxsZtt, KgxsZuXM
answer:
xsZ


question:
VutZiVkDQcVpQO, BDQVDyBdiVkDQcVpuvNN
answer:
iVkDQcVp


question:
VOUUgPfdkKWHMemvWv, wuJfdkKWHMjGgrPP
answer:

fdkKWHM