instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
lMRuEThD, wqQRuEKp
answer:
RuE


question:
rCFrfkmXbSHK, mztfkmXwez
answer:
fkmX


question:
oiNEYHxbvAb, bcDDdEYHxbCREd
answer:

EYHxb