Let $a$ and $b$ be positive real numbers such that $a + b = 1.$  Find set of all possible values of $\frac{1}{a} + \frac{1}{b}.$
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Let $a$ and $b$ be positive real numbers such that $a + b = 1.$  Find set of all possible values of $\frac{1}{a} + \frac{1}{b}.$
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
[4,\infty)
Let $a$ and $b$ be positive real numbers such that $a + b = 1.$  Find set of all possible values of $\frac{1}{a} + \frac{1}{b}.$
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