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

Example Input: STvKOHq, XMGvKOdyM
Example Output: vKO

Example Input: wYhGWdRC, cFGWdHEy
Example Output: GWd

Example Input: qQkmYsYN, UhkmYHSy
Example Output:
kmY