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

Example Input: uqDaPS, XyDaMZ
Example Output: Da

Example Input: jJSSBmflUyrEMLjSycA, YkmujkSSBmflUyrKKJZ
Example Output: SSBmflUyr

Example Input: JpgnEFShkxpt, KnnEFShom
Example Output:
nEFSh