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

Example Input: yrIDSuVuQU, UXTSuVuLcch
Example Output: SuVu

Example Input: CiElmOvTqJGVJkfSaDRzE, EjDJwMyxTvTqJGVJkfluB
Example Output: vTqJGVJkf

Example Input: SPqsfHSNg, vJcDhqsfHSjgsU
Example Output:
qsfHS