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: NTINFnRckGsfLqhSoA, UUONcKKFnRckGsfLqVak
Example Output: FnRckGsfLq

Example Input: XXermyNhqOMsb, rBPyNhqOhdIa
Example Output:
yNhqO