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

Example Input: wLLwjL, arLwXm
Example Output: Lw

Example Input: TvNVpHLPYjBCeUpyxlzFZ, tgKdPKVYjBCeUpyPK
Example Output: YjBCeUpy

Example Input: XKdhdDjf, nMVhdDRK
Example Output:
hdD