instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
xfZYYDKEqoRRu, ztCeYYDKEqoPG
answer:
YYDKEqo

question:
LiiFMMLGfNHVnnga, beXMMLGfNHVsjdfdN
answer:
MMLGfNHV

question:
CSvptSngkVHX, kLKptSngkivt
answer:
ptSngk