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

Example Input: TvNVpHLPYjBCeUpyxlzFZ, tgKdPKVYjBCeUpyPK
Example Output: YjBCeUpy

Example Input: NNpkdhvgT, BMkAkdhvrwV
Example Output: kdhv

Example Input: sCHywMTJLfytmzR, iZOHywMTJLfylYGzVvQNz
Example Output:
HywMTJLfy