solution: A number is congruent to the sum of its digits $\pmod 9$. Thus, \begin{align*}
  &1+12+123+1234+12345+123456\\
  &\qquad+1234567+12345678\\
  &\quad\equiv 1+3+6+10+15+21+28+36\pmod 9 \\
  &\quad\equiv 1+3+6+1+6+3+1+9\pmod 9 \\
  &\quad\equiv 30\pmod 9 \\
  &\quad\equiv \boxed{3}\pmod 9.
  \end{align*}
prompt.content: <|im_start|>system
  You are a helpful assistant.<|im_end|>
  <|im_start|>user
  If $$1+12+123+1234+12345+123456+1234567+12345678$$is congruent to $n$ modulo 9, where $0\le n<9$, what is the value of $n$?
  Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
  <|im_start|>assistant
  
prompt.role: user
extra_info.answer: 3
extra_info.question: If $$1+12+123+1234+12345+123456+1234567+12345678$$is congruent to $n$ modulo 9, where $0\le n<9$, what is the value of $n$?
extra_info.split: test