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

Example Input: MSxTzCpiJAplpzSvLlNJS, oScCpiJAplpNVrqkn
Example Output: CpiJAplp

Example Input: lsNwypFwhKP, diEfLwypFwEKqCN
Example Output: wypFw

Example Input: HXYkGv, GCYksu
Example Output:
Yk