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

Example Input: JIOKyo, oPOKsX
Example Output: OK

Example Input: BfCCzPNLBbwCoxMVAG, vhwNLBbwCbH
Example Output: NLBbwC

Example Input: bhJEQohIHycSxDHOvDqA, GeRQYnihIHycSxDaD
Example Output:
hIHycSxD

