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

Example Input: ktABEFESAVHZkkY, uMjxiESAVHZkZgWUte
Example Output: ESAVHZk

Example Input: JqdTDnZqSuSVcMsx, TEtDDnZqSuZa
Example Output: DnZqSu

Example Input: rRmkmETbjzCzZZxihrVdefxfcenJ, ogQtzAgWjKCzZZxihrVdRswMCmngp
Example Output:
CzZZxihrVd