instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
yxJxNRLEnKGHziJtfb, KfReWhEnKGHzitzfPWzK
answer:
EnKGHzi


question:
fdxgzAMP, xrcxgzYW
answer:
xgz


question:
GUyKSsDoqTx, ztyKSsDfb
answer:

yKSsD