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

zfUPUDeKbCMQa, BkAJFJUDeKbCMZmkFu
UDeKbCM

zmbmQuyNGOe, mUMEmQuyiuS
mQuy

ELtaSfXJlEkuzyxw, XqfXJlEkigh

fXJlEk