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

Example Input: HhBhJMpxpty, MxTJMpxnQEf
Example Output: JMpx

Example Input: CzkPtkpMTDeNZwCPbJJn, HzpMVDeNZwCPbJVOU
Example Output: DeNZwCPbJ

Example Input: wtszqfaWxcaWCwZMoY, SxdhBxWxcaWCwcVUeD
Example Output:
WxcaWCw