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

Example Input: iYuUgULgqcAgd, kRNUgULgqFv
Example Output: UgULgq

Example Input: AedXEOrEgvnzF, TVTEOrEgvxKuJgv
Example Output: EOrEgv

Example Input: ZxXQtF, aCXQcY
Example Output:
XQ