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

Example Input: iYuUgULgqcAgd, kRNUgULgqFv
Example Output: UgULgq

Example Input: qMnjlfIsQRtUlPggCpHqu, gfVndMwYDIsQRtUlPgqBJKCX
Example Output: IsQRtUlPg

Example Input: AxAmDG, LTAmEV
Example Output:
Am