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

Example Input: ICizmXnKMpUH, oDrnmXnKgWXX
Example Output: mXnK

Example Input: OVZxWYzAAxG, rStOxWYzJeoC
Example Output: xWYz

Example Input: eeAuIFWxPiFibSlELTv, iMfmsxxPiFibSlEpq
Example Output:
xPiFibSlE