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

Example Input: nxoXDohHr, WcbkXDohFbJ
Example Output: XDoh

Example Input: osmJJcZlDAXBgJFsJKa, rzPNlDAXBgJYrgXlH
Example Output: lDAXBgJ

Example Input: gSaPMW, MuaPgr
Example Output:
aP