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

Example Input: zBNTHKtofMdHfBgJhOfojzM, VIkVdFapofMdHfBgjPCUo
Example Output: ofMdHfBg

Example Input: AedXEOrEgvnzF, TVTEOrEgvxKuJgv
Example Output: EOrEgv

Example Input: OYTGuLStHtNkKjS, xchrLkGuLStHZySq
Example Output:
GuLStH