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

Example Input: DGvUCrUVlUnQBShkWnfnceGasvI, NfzGUnQBShkWnpLMnY
Example Output: UnQBShkWn

Example Input: koddLvYmRXDUuUnW, GnqDYGmmRXDUuUquAnf
Example Output: mRXDUuU

Example Input: CTLAtxvktJfE, VqAtxvktfeCZ
Example Output:
Atxvkt