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

Example Input: zfUPUDeKbCMQa, BkAJFJUDeKbCMZmkFu
Example Output: UDeKbCM

Example Input: UovaYpHjYSQzrfsxRfvIZE, pUOFxIKOGQzrfsxRfvIjrza
Example Output: QzrfsxRfvI

Example Input: ixyjFRhXjAnScOh, HPnBRhXjAnScdh
Example Output:
RhXjAnSc