instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
feYKRk, PrYKMW
answer:
YK


question:
HqaOvLaZbs, RifOvLaZkh
answer:
OvLaZ


question:
ZvRxZxUOyjaalK, YyqHqHRxZxUOyiTHa
answer:

RxZxUOy