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

Example Input: rduIwWNGM, AJqYIwWNaCap
Example Output: IwWN

Example Input: MriFNpGM, yaiFNduk
Example Output: iFN

Example Input: PXbGbCw, nabGbEcv
Example Output:
bGb