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

[EX Q]: mRVieYomZqJXaTDsShCyfPW, ifOAlnptmZqJXaTDsVMqY
[EX A]: mZqJXaTDs

[EX Q]: QjDQjzAIsnYgNmmetl, vyqDQjzAIsnNajYEheP
[EX A]: DQjzAIsn

[EX Q]: HhRRJs, ZQRRBM
[EX A]:
RR