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

Example Input: EyvnjbVLF, vqnjblzR
Example Output: njb

Example Input: fVEFJa, WtEFYK
Example Output: EF

Example Input: OUNqomxFcLXhWdfB, gdqomxFcLHQPCu
Example Output:
qomxFcL