instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
njzfcapS, JDzfcYQh
answer:
zfc


question:
rCFrfkmXbSHK, mztfkmXwez
answer:
fkmX


question:
kjiOtk, tciOpB
answer:

iO