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: RwduMBkDazrwZP, UPzcwtWMBkDazrAw
Example Output: MBkDazr

Example Input: RPNQAeATlQadMpVDW, NSpkgQAeATlQpzroBP
Example Output:
QAeATlQ