instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
QqtCFzXHPNFXx, XECFzXHPSGwUuk
answer:
CFzXHP


question:
yRhCObvPZYoKUoQnyaatR, NHzLJYPZYoKUoQnJnIsZxC
answer:
PZYoKUoQn


question:
jMKWESgGtTvCxpetDCobhYt, nFrwGtTvCxpetDKzQUBV
answer:

GtTvCxpetD