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: OyrqfQQnzOFUzrkDM, iBkQQnzOFewhjvO
Example Output: QQnzOF

Example Input: nxoXDohHr, WcbkXDohFbJ
Example Output:
XDoh