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

Example Input: SUgXyznbUQRpiLUTlRb, jlnwLTnbUQRpioUFyJ
Example Output: nbUQRpi

Example Input: jkGcUm, dxGcSI
Example Output: Gc

Example Input: qZADGzoLuJfbsLoty, cMnGoLuJfbsLoboqou
Example Output:
oLuJfbsLo