instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
spGRUmIYuGl, qkqRUmItqU
answer:
RUmI


question:
krnkpodgfpCKtfCqyzUbymWbxi, DydgSWpCKtfCqyzDaMsjqc
answer:
pCKtfCqyz


question:
SHZYvmrFv, OxPZYvmriKsW
answer:

ZYvmr