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

Example Input: BTvLVMYp, mjOvLVMqYo
Example Output: vLVM

Example Input: jFVaEHbMrrkW, ekfVaEHbPnBnM
Example Output: VaEHb

Example Input: POGSstKcm, VsSstdaZ
Example Output:
Sst