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

Example Input: KvPFobZEGs, eKFobZEtnm
Example Output: FobZE

Example Input: CCzKRbuEAmN, qTLzKRbuhEqq
Example Output: zKRbu

Example Input: gcZobbOQjatXRBv, WBqhvtlobbOQjatXXwPAAt
Example Output:
obbOQjatX