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

jLbHvZmecfxMcGLXGVsO, erFBGmecfxMcJtDyKGZ
mecfxMc

iwSQnplQZFbXQ, lHWnplQZFzswgU
nplQZF

ivyXNjObnIQAJIrvmvUHhC, JHSSnIQAJIrvdY

nIQAJIrv