In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.

[EX Q]: UtUSmsOI, dCUSmGoQ
[EX A]: USm

[EX Q]: nFgMXUzpStDAybiwm, aNJrXUzpStDjp
[EX A]: XUzpStD

[EX Q]: WbSHqX, hHSHnG
[EX A]:
SH