instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
NwmTIZSnlKGG, qAYIZSnfWRd
answer:
IZSn


question:
vMYfFo, EHYfnP
answer:
Yf


question:
ZJITowpTbFcIbWZOVGK, avzTbFcIbWaMljGjC
answer:

TbFcIbW