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

Example Input: yRhCObvPZYoKUoQnyaatR, NHzLJYPZYoKUoQnJnIsZxC
Example Output: PZYoKUoQn

Example Input: eFUexDIFlaPDUwrOb, mTvkKGUxDIFlaPDUwxGVpnIwbi
Example Output: xDIFlaPDUw

Example Input: JxPHzSmbu, CzPHzSpq
Example Output:
PHzS