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:
fVEFJa, WtEFYK
answer:
EF


question:
qKvQtHAJjqLHHDWuPSJuBrnc, lHahsqLHHDWuPSJSBZMmbe
answer:

qLHHDWuPSJ