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

Q: RwduMBkDazrwZP, UPzcwtWMBkDazrAw

A: MBkDazr
****
Q: XeQwOS, OuQwNR

A: Qw
****
Q: LPGQBfTh, yQIGQBQrl

A:
GQB
****