instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
HhBhJMpxpty, MxTJMpxnQEf
answer:
JMpx


question:
feYKRk, PrYKMW
answer:
YK


question:
qgWffUaZmZ, aNffUavtEl
answer:

ffUa