instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
FgQsxN, UMQsIa
answer:
Qs


question:
ksRxEVrz, cOMRxEViwF
answer:
RxEV


question:
umONWy, kWONpe
answer:

ON