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

Example Input: qczzCr, zDzzUI
Example Output: zz

Example Input: BVipiZoGXaWdjmDsxWP, yxppsiYkiZoGXaWdjoDRuKW
Example Output: iZoGXaWdj

Example Input: YZPsxjUb, OQPsxRQ
Example Output:
Psx