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

Example Input: vSFxjd, AHFxpi
Example Output: Fx

Example Input: OhMVLbQhBxEaOZY, iDVLbQhBxBiiD
Example Output: VLbQhBx

Example Input: lpWEGmpssYpUNVl, DWKEGmpssuTULv
Example Output:
EGmpss