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

Example Input: WTnsmP, INnsIM
Example Output: ns

Example Input: CzkPtkpMTDeNZwCPbJJn, HzpMVDeNZwCPbJVOU
Example Output: DeNZwCPbJ

Example Input: ACbPidPcF, vxPidkC
Example Output:
Pid