instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
QgkpBHsrfRYJCa, AdjbKLpBHsrfbpBC
answer:
pBHsrf


question:
wYhGWdRC, cFGWdHEy
answer:
GWd


question:
sLnZxY, xnnZcF
answer:

nZ