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

Example Input: VpJvIZdkzKovjc, BZEizZdkzKYZ
Example Output: ZdkzK

Example Input: gTjTwC, OUjTgM
Example Output: jT

Example Input: lkFGXvTkKm, wwELXvTkcOnG
Example Output:
XvTk