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

Example Input: zmbmQuyNGOe, mUMEmQuyiuS
Example Output: mQuy

Example Input: koddLvYmRXDUuUnW, GnqDYGmmRXDUuUquAnf
Example Output: mRXDUuU

Example Input: tZQkYeNZXZFRc, LxOleNZXZbAfa
Example Output:
eNZXZ