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

Example Input: spGRUmIYuGl, qkqRUmItqU
Example Output: RUmI

Example Input: goyZUz, QryZlD
Example Output: yZ

Example Input: noFWVjZKhnEWe, HVhWVjZKHFq
Example Output:
WVjZK

