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

Example Input: TizkNtJUPHfhmGQ, enzehVkNtJUPHunpG
Example Output: kNtJUPH

Example Input: vMYfFo, EHYfnP
Example Output: Yf

Example Input: QXdiuvwjsnnc, andiuvwjCmqPS
Example Output:
diuvwj