instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
NxgzLSzFGa, JvLzLSzsuj
answer:
zLSz


question:
rszjOPpbXm, pnBujOPpWHz
answer:
jOPp


question:
yXQgAu, dtQgtG
answer:

Qg