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

Example Input: UvYbfKFybXofcwLRrLRiK, BgMZKFybXofcVe
Example Output: KFybXofc

Example Input: OXdSmcKG, XbDdSmJl
Example Output: dSm

Example Input: JtIohuvwlmoUdoJIE, rEuvwlmoOhj
Example Output:
uvwlmo