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

Ex Input:
HXYkGv, GCYksu

Ex Output:
Yk


Ex Input:
QeNePjbLBKbDOuAVTJtXL, xjPVOyPbLBKbDOuDsMSEF

Ex Output:
bLBKbDOu


Ex Input:
XmvorKmzTlQlDZHQHfnA, HWjzTlQlDZHQuMXovSWuM

Ex Output:

zTlQlDZHQ