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

lkFGXvTkKm, wwELXvTkcOnG
XvTk

SJIkEibGrqcrOBgGjYjJc, EervOGrqcrOBgGJZyx
GrqcrOBgG

OqMEeDXIZTBZPVf, jYAqeDXIZTNsbbOr

eDXIZT