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

Example Input: yITbYie, TlqTbYomH
Example Output: TbY

Example Input: AeYjeKwZQillzpD, SnqviKwZQillrxuTB
Example Output: KwZQill

Example Input: eJdHLluWhp, XBLbdHLluVDqBk
Example Output:
dHLlu