instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
xtCJGe, DXCJSw
answer:
CJ


question:
BrDGrTD, PBHDGrDw
answer:
DGr


question:
HffcxqvRoCWNNKJVxbCnKKC, LORoCWNNKJKvRo
answer:

RoCWNNKJ