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

Ex Input:
BrDGrTD, PBHDGrDw

Ex Output:
DGr


Ex Input:
spGRUmIYuGl, qkqRUmItqU

Ex Output:
RUmI


Ex Input:
pCYgDx, OVYgcv

Ex Output:

Yg