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

Example Input: yQRDycTycwH, ImycTycrR
Example Output: ycTyc

Example Input: OgWFOfjNYmXVjBBvOdunIc, eGljKGnzFKFOfjNYmXVjdlqsT
Example Output: FOfjNYmXVj

Example Input: pSKXOC, nAKXWO
Example Output:
KX