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

Example Input: ZRjPgqbLL, uIsmPgqbBB
Example Output: Pgqb

Example Input: GrvtMjEvRlmN, ifGOWMjEvRPSOZK
Example Output: MjEvR

Example Input: hJxKVW, uAxKpY
Example Output:
xK