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

Example Input: CUlMsvov, iflMsSRp
Example Output: lMs

Example Input: UTdardKNThdYrGKMqZPeg, mvrThdYrGKMlcCxBtak
Example Output: ThdYrGKM

Example Input: MTyIoTOG, jUIoTKNY
Example Output:
IoT