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

Example Input: SJIkEibGrqcrOBgGjYjJc, EervOGrqcrOBgGJZyx
Example Output: GrqcrOBgG

Example Input: jXqEDHTCxTiUAICWZJdpmYq, GBTCxTiUAICZKnLgZBXi
Example Output: TCxTiUAIC

Example Input: mkXHxYsnFCaUFyxzvkYBOejd, uZwJqumdzjYsnFCaUFyxostLYOaW
Example Output:
YsnFCaUFyx