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

Example Input: XmiLktrUjJDOCJ, UIKrUjJDOQsR
Example Output: rUjJDO

Example Input: nrIHKzJCdAQzUDRBYpg, JDzJCdAQzUMMYrLcfO
Example Output: zJCdAQzU

Example Input: qvmvxBVP, fAhmvxPSV
Example Output:
mvx