instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
slTUxy, oqTUYa
answer:
TU


question:
nWTnWqkLqYTBxT, cSTnWqkLqYwXmxRF
answer:
TnWqkLqY


question:
FrIYjdvS, YNZIYjdgzQM
answer:

IYjd