instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
rqhQxQQDdYwemFiiwcfVx, cEQDdYwemFtwpfNJC
answer:
QDdYwemF


question:
CUxfOt, dyxfNp
answer:
xf


question:
HdZeKNLUySizuLbuby, LDQaBjxrpZeKNLUySizdNYwoagB
answer:

ZeKNLUySiz