What is the ones digit of $1 \cdot 3 \cdot 5 \cdot 7 \cdot 9 \cdot 11 \cdot 13$?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
What is the ones digit of $1 \cdot 3 \cdot 5 \cdot 7 \cdot 9 \cdot 11 \cdot 13$?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
5
What is the ones digit of $1 \cdot 3 \cdot 5 \cdot 7 \cdot 9 \cdot 11 \cdot 13$?
train