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

Example Input: kWnjCoVmCSVuW, RILPKCoVmCSVbaOza
Example Output: CoVmCSV

Example Input: TUAHhdvHIBxogI, LjfGsAHhdvHJcSdNV
Example Output: AHhdvH

Example Input: gjGvfT, pnGvnk
Example Output:
Gv