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

Example Input: nuwMzarLqoPvabJla, JKcrLqoPvabJNDCILGQ
Example Output: rLqoPvabJ

Example Input: mCxQTIaXN, mWQTIaxzPT
Example Output: QTIa

Example Input: yMujEmkaXXkKhGxcO, mDpqmkaXXkAdRZDJ
Example Output:
mkaXXk