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

Example Input: lrBJDRkT, jmBJDrI
Example Output: BJD

Example Input: UIjAMFDuxDDGkfQa, VdsHuxDDGkfZHZZ
Example Output: uxDDGkf

Example Input: MaXWarfEqZhQxKXSpFziGJa, TqMeKJkqZhQxKXSpmb
Example Output:
qZhQxKXSp