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

Example Input: feYKRk, PrYKMW
Example Output: YK

Example Input: koddLvYmRXDUuUnW, GnqDYGmmRXDUuUquAnf
Example Output: mRXDUuU

Example Input: XfyCaWeGqGiyLgVHPpVgbjRqkM, LhfyWOoqqGiyLgVHPhQ
Example Output:
qGiyLgVHP