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: BUvWkxrAvDQG, rHrkxrAkCE
Example Output: kxrA

Example Input: vGADFaF, kQADFXNf
Example Output:
ADF