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

Example Input: rcKVmDzwJKeK, uYqmDzwJKxkGi
Example Output: mDzwJK

Example Input: iUtNuU, iKtNWk
Example Output: tN

Example Input: pERFqMkAANae, uHmrFYFqMkAADbC
Example Output:
FqMkAA