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

Example Input: nTAXUw, OWAXYU
Example Output: AX

Example Input: nxoXDohHr, WcbkXDohFbJ
Example Output: XDoh

Example Input: PHIymSZaQtCmvzBCWIm, KGCoRaQtCmvzBZZAudJc
Example Output:
aQtCmvzB