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

Example Input: eeoJEtGHPDvHck, ezPGHPDvHSf
Example Output: GHPDvH

Example Input: GoodBOwvrki, kRCsdBOwvrakgiH
Example Output: dBOwvr

Example Input: IIsEsWNxuPmTfkPX, iMWNxuPmFGtt
Example Output:
WNxuPm