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

Example Input: AxAmDG, LTAmEV
Example Output: Am

Example Input: egYXVtCPvWxP, VMOolyVtCPvWjIx
Example Output: VtCPvW

Example Input: dSmYOKxuGgVJboDCY, GCfNjCYOKxuGgVfB
Example Output:
YOKxuGgV