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

Example Input: XHqQIPw, brqQIkAt
Example Output: qQI

Example Input: gwVLygvd, VOQLyglfo
Example Output: Lyg

Example Input: KwcjcXFMMSOXZGGTpn, TuFMMSOXZGyj
Example Output:
FMMSOXZG