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

Example Input: wbdHVigIkjNkuAmbr, iSgIkjNkQYyn
Example Output: gIkjNk

Example Input: SFQHJlK, dHfQHJoUC
Example Output: QHJ

Example Input: wtPbBLPMXgFUZuIiMXdllkBJroWJB, BEXePuCugFUZuIiMXdUpKvh
Example Output:
gFUZuIiMXd