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

Example Input: BrDGrTD, PBHDGrDw
Example Output: DGr

Example Input: JXnHYuZvAYK, zhUYuZvASGhd
Example Output: YuZvA

Example Input: uxcXZLVEoJk, qsxZLVEtUvV
Example Output:
ZLVE