instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
xQcYRVFFqrVAMsBm, VErcKZvcYRVFFqzKo
answer:
cYRVFFq


question:
YXsgPE, ENsgSO
answer:
sg


question:
uLkBea, MrkBIp
answer:

kB