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

Example Input: eMDNXl, ZZDNAa
Example Output: DN

Example Input: yQRDycTycwH, ImycTycrR
Example Output: ycTyc

Example Input: eOwrwgfnEXcCNOLsifOxXvp, bLskrwgfnEXcCNqOe
Example Output:
rwgfnEXcCN