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

Example Input: STvKOHq, XMGvKOdyM
Example Output: vKO

Example Input: yQRDycTycwH, ImycTycrR
Example Output: ycTyc

Example Input: pKlOrDdHMsJAXVlYpKh, HjqCZHMsJAXVlsi
Example Output:
HMsJAXVl