Let $f(x) = x^2 - 4\sqrt{x} + 1$. What is $f(f(4))$?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Let $f(x) = x^2 - 4\sqrt{x} + 1$. What is $f(f(4))$?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
70
Let $f(x) = x^2 - 4\sqrt{x} + 1$. What is $f(f(4))$?
train