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

Example Input: zeuyZKwvIOfx, BlmZKwvspUt
Example Output: ZKwv

Example Input: JjEQVKijeyEQ, dwSVKijeywCTvb
Example Output: VKijey

Example Input: qAQCRBJttCHRvLHRw, EXshgfJttCHRjNvG
Example Output:
JttCHR