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

Example Input: CMrTXnTnTVaR, srnXnTnTDNULO
Example Output: XnTnT

Example Input: iupYjFXrrMqWzJSLUSwmEukHc, hqajjWrrMqWzJSLnF
Example Output: rrMqWzJSL

Example Input: GknPxBJiAYvxJDVNITwNRx, nPGkVziAYvxJDVNIRCSXPF
Example Output:
iAYvxJDVNI