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

Example Input: GlAYDsKQoXy, IxDsKQuK
Example Output: DsKQ

Example Input: QjDQjzAIsnYgNmmetl, vyqDQjzAIsnNajYEheP
Example Output: DQjzAIsn

Example Input: RWVriDBLFGqTHkndkiVy, zuKNasDBLFGqTHknFeDdylnVlP
Example Output:
DBLFGqTHkn