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

Q: EPUxsZtt, KgxsZuXM

A: xsZ
****
Q: VLxrvK, gvxrac

A: xr
****
Q: XWKEpwGRkfCFZGOyZQOoypx, lhQkmVqeRkfCFZGOyugPLqs

A:
RkfCFZGOy
****