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

Example Input: nXVXIEGP, fkXIEkU
Example Output: XIE

Example Input: xzMUdHcoYJFWLOILjrg, vCscoYJFWLzO
Example Output: coYJFWL

Example Input: YPeBvuJXaSLLPhKpUQ, ryjPdyuJXaSLLPhIzBeJP
Example Output:
uJXaSLLPh