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

Example Input: SQNzngllNbOkKDK, MijfNzngllNDfWge
Example Output: NzngllN

Example Input: vMYfFo, EHYfnP
Example Output: Yf

Example Input: MzAyQJsZUDWjBZqV, TRYRQJsZUDWeg
Example Output:
QJsZUDW