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

Example Input: uGDJixAmSiVaFRmfKRM, NsTGxsJixAmSiVageSw
Example Output: JixAmSiVa

Example Input: iJbjApY, ggwbjAws
Example Output: bjA

Example Input: KcvDFG, YXvDEd
Example Output:
vD