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

Example Input: mCxQTIaXN, mWQTIaxzPT
Example Output: QTIa

Example Input: qQkmYsYN, UhkmYHSy
Example Output: kmY

Example Input: FqivzQYyaFqM, COOvzQYyQftk
Example Output:
vzQYy