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

Example Input: spUbdWDLWCeqr, vIuHkWDLWCQEPaz
Example Output: WDLWC

Example Input: rRmkmETbjzCzZZxihrVdefxfcenJ, ogQtzAgWjKCzZZxihrVdRswMCmngp
Example Output: CzZZxihrVd

Example Input: QBRqJq, bjRqlq
Example Output:
Rq