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: DnAzbgMtdPKsNCMpBfc, QdfXRkWREzbgMtdPKsGx
Example Output: zbgMtdPKs

Example Input: aWshKwEuYBBdSwIAyXw, wfVuYBBdSwIAseTxR
Example Output:
uYBBdSwIA