instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
fdxgzAMP, xrcxgzYW
answer:
xgz


question:
VLxrvK, gvxrac
answer:
xr


question:
QRVLXytPPIJGqiqCUyXaakIvR, aHCPIJGqiqCULTtbbgA
answer:

PIJGqiqCU