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

Example Input: RwduMBkDazrwZP, UPzcwtWMBkDazrAw
Example Output: MBkDazr

Example Input: UiaECWZf, gRyaECWLGRl
Example Output: aECW

Example Input: aPwxDStQefTY, CRtDStQlUW
Example Output:
DStQ