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

Example Input: OUNqomxFcLXhWdfB, gdqomxFcLHQPCu
Example Output: qomxFcL

Example Input: eMDNXl, ZZDNAa
Example Output: DN

Example Input: TjGnDFCkyGPPvKZ, BPvDFCkyGPir
Example Output:
DFCkyGP