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

[EX Q]: JIOKyo, oPOKsX
[EX A]: OK

[EX Q]: yiKkIxbKvNk, znaIxbKggg
[EX A]: IxbK

[EX Q]: aIFHNy, pSFHvq
[EX A]:
FH