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

[EX Q]: rqhQxQQDdYwemFiiwcfVx, cEQDdYwemFtwpfNJC
[EX A]: QDdYwemF

[EX Q]: zqwhMdAdXQfQCAmVNaYZm, toYMIwQeadAdXQfQCAmLyheFOv
[EX A]: dAdXQfQCAm

[EX Q]: DZXgcPUpm, AUPXgcPULx
[EX A]:
XgcPU