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

Example Input: euQWhCovKplukMYznXcD, XAfMhKdzhCovKplukMcMlSuBw
Example Output: hCovKplukM

Example Input: QEEVsnbQIgrxaZmflaZ, dPSbljkdQIgrxaZmgVzMT
Example Output: QIgrxaZm

Example Input: pFZFIZeP, WbkZFIRD
Example Output:
ZFI