The sum of four two-digit numbers is 221. None of the eight digits is $0$ and no two of them are the same. Which of the digits $1$ through $9$ does not appear in one of the four two-digit numbers?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
The sum of four two-digit numbers is 221. None of the eight digits is $0$ and no two of them are the same. Which of the digits $1$ through $9$ does not appear in one of the four two-digit numbers?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
4
The sum of four two-digit numbers is 221. None of the eight digits is $0$ and no two of them are the same. Which of the digits $1$ through $9$ does not appear in one of the four two-digit numbers?
train