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

Example Input: nYoRQU, gQoRZQ
Example Output: oR

Example Input: hVQJkZyKfPoOQEukfAbXDpB, qpojyxWkZyKfPoOQEZkUI
Example Output: kZyKfPoOQE

Example Input: pKLUwFJeHsNvGcgznveyhDjf, ORcHsNvGcgztM
Example Output:
HsNvGcgz