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

Example Input: bdCOjNchdKtvWzOI, FwejNchdKhEd
Example Output: jNchdK

Example Input: YPeBvuJXaSLLPhKpUQ, ryjPdyuJXaSLLPhIzBeJP
Example Output: uJXaSLLPh

Example Input: VWcgFL, VfcgJQ
Example Output:
cg