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: apGMPThLTCw, LvMPThYW
Example Output: MPTh

Example Input: HsSgltmChBxqDyDtc, CDPoOiChBxqDyDURIrF
Example Output:
ChBxqDyD