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

Example Input: vJtmxQmHEq, yobgAtmxQmMeoLz
Example Output: tmxQm

Example Input: bmZKWkYPqugcvzbHykblPzQLhK, tPUzKqugcvzbHypzk
Example Output: qugcvzbHy

Example Input: EWtqsCfFgtQPIdP, ptFfoOqsCfFgutOTb
Example Output:
qsCfFg