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

Example Input: PivhPfah, XSghPfOi
Example Output: hPf

Example Input: nFgMXUzpStDAybiwm, aNJrXUzpStDjp
Example Output: XUzpStD

Example Input: glbghmYZbaSZDM, coFPpbghmYZbahDLquQee
Example Output:
bghmYZba