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

Example Input: VRXUhOYfTul, JqZUhOYKq
Example Output: UhOY

Example Input: UovaYpHjYSQzrfsxRfvIZE, pUOFxIKOGQzrfsxRfvIjrza
Example Output: QzrfsxRfvI

Example Input: wvenYCYTW, oPBjenYCYRI
Example Output:
enYCY