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

Example Input: HaLZdTX, tLLZdEXN
Example Output: LZd

Example Input: iYuUgULgqcAgd, kRNUgULgqFv
Example Output: UgULgq

Example Input: qVdPGVxtyJSzXBAXl, jrFdPGVxtyJSuoZxlOC
Example Output:
dPGVxtyJS