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

Example Input: OYERnjubLFovtcS, FngzQJVGERnjubLFafmzq
Example Output: ERnjubLF

Example Input: VutZiVkDQcVpQO, BDQVDyBdiVkDQcVpuvNN
Example Output: iVkDQcVp

Example Input: YlKurYp, RKQKurrc
Example Output:
Kur