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

[EX Q]: xQcYRVFFqrVAMsBm, VErcKZvcYRVFFqzKo
[EX A]: cYRVFFq

[EX Q]: wbFDXJQDQxQJzudOUlR, QEbsIDXJQDQxQsSYIutwU
[EX A]: DXJQDQxQ

[EX Q]: dALxfuP, usLxfUuA
[EX A]:
Lxf