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

Example Input: HqaOvLaZbs, RifOvLaZkh
Example Output: OvLaZ

Example Input: XeQwOS, OuQwNR
Example Output: Qw

Example Input: eHJVvkpgczSpVSei, CkMakpgczSpVhSDtgiT
Example Output:
kpgczSpV