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

Example Input: DwLGzwYOWjtzIunE, TTViSbkwYOWjtzNqUOOz
Example Output: wYOWjtz

Example Input: FQAznAuFjoBKRKB, hPmtFFPnuAznAuFjoBKTgkeJyjcd
Example Output: AznAuFjoBK

Example Input: iMrvMcny, VsrvMWIV
Example Output:
rvM