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

[EX Q]: qQkmYsYN, UhkmYHSy
[EX A]: kmY

[EX Q]: RtAchtNymcswVk, FWRuRchtNymcswUkoERHyML
[EX A]: chtNymcsw

[EX Q]: FWHluAcvGynmDFnWF, wBIGacvGynmDIBYaSs
[EX A]:
cvGynmD