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

Example Input: ahPbomjSH, rBbomynK
Example Output: bom

Example Input: mXHhaCEIwqwEZcz, JZPXbYHhaCEIwZmna
Example Output: HhaCEIw

Example Input: CQDLqaUhJvTZyCHtmXjxF, fOAWZGNLLqaUhJvTZyRXuis
Example Output:
LqaUhJvTZy