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

QgkpBHsrfRYJCa, AdjbKLpBHsrfbpBC
pBHsrf

SJIkEibGrqcrOBgGjYjJc, EervOGrqcrOBgGJZyx
GrqcrOBgG

aqcKQOAPiGDkVyzDWVYQGw, cIRAPiGDkVyfBlmVH

APiGDkVy