instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
cUCQXEFSgRZjK, RYdvUQXEFSgRZVlwx
answer:
QXEFSgRZ


question:
cvZfWOwa, xOfWOhZs
answer:
fWO


question:
GQWGuxatkfIHqsD, SofTxatkfIJPTtjI
answer:

xatkfI