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

Example Input: oGaGjsaKsUpLQAg, iDGjsaKsUoYGuta
Example Output: GjsaKsU

Example Input: DQBpdnwVDcnCDEWpD, gAtCdnwVDcnCYv
Example Output: dnwVDcnC

Example Input: hROqRkVZMdKmZ, vzZiRGOqRkVZMdKiYz
Example Output:
OqRkVZMdK