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

XZslQqrShfCXRXyHrFVq, BtOQgQqrShfCXRRCRbMvXPM
QqrShfCXR

spUbdWDLWCeqr, vIuHkWDLWCQEPaz
WDLWC

uoghyKeBCVSfRqUciOHH, hkMPrQHdKeBCVSfRqUNxWTeY

KeBCVSfRqU