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

Example Input: lMRuEThD, wqQRuEKp
Example Output: RuE

Example Input: kIBDjQLEZepVNHqnKqhine, hTZepVNHqnYTajyzv
Example Output: ZepVNHqn

Example Input: EClJcgHpkQUTXxfuOVFHO, mzHJcgHpkQUTidp
Example Output:
JcgHpkQUT