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

Example Input: zRwQdelc, UdAUwQdejhe
Example Output: wQde

Example Input: YXsgPE, ENsgSO
Example Output: sg

Example Input: YCAyruPTTHWhCYaiXfIl, OETdzqAyruPTTHWgS
Example Output:
AyruPTTHW