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

Example Input: jdLbZSCzaAHGbNwILGmudOH, RdIPuEYJvUZSCzaAHGbNduLToRC
Example Output: ZSCzaAHGbN

Example Input: eeoJEtGHPDvHck, ezPGHPDvHSf
Example Output: GHPDvH

Example Input: aXQcPFmGxlPclB, JjOaQcPFmGDanBNz
Example Output:
QcPFmG