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

Example Input: PShMbsbexXGlpBuMMDZZS, sVqGxSexXGlpBxuHXoI
Example Output: exXGlpB

Example Input: PivhPfah, XSghPfOi
Example Output: hPf

Example Input: mXdkwiOWUVvLHSIDaz, gakwiOWUVvARLNcn
Example Output:
kwiOWUVv