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

Example Input: rRmkmETbjzCzZZxihrVdefxfcenJ, ogQtzAgWjKCzZZxihrVdRswMCmngp
Example Output: CzZZxihrVd

Example Input: rCFrfkmXbSHK, mztfkmXwez
Example Output: fkmX

Example Input: ixTVfG, TbTVte
Example Output:
TV