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

Example Input: gTjTwC, OUjTgM
Example Output: jT

Example Input: HiEuutntEBpU, fdkqEuutntEBABdGZRND
Example Output: EuutntEB

Example Input: Zhkcjb, ABkcFH
Example Output:
kc