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: YCAyruPTTHWhCYaiXfIl, OETdzqAyruPTTHWgS
Example Output: AyruPTTHW

Example Input: JsJdEv, UhJdaH
Example Output:
Jd