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:
KfjqnJLciTXqkJK, yqfRcfqnJLcisSB
answer:
qnJLci


question:
HKivZfqXUmD, ZNvZfqXUIAsnt
answer:

vZfqXU