Yearly polynomial

Consider the following polynomial:

$f(x)=\sum_{i=0}^{2015} a_ix^{2i}$

The sequence $\{a_i\}_{i=0}^{i=2015}$ is a sequence of arbitrary constants for $f(x)$ .

Find the sum of all $\textbf{real}$ roots of the given polynomial.

$\textbf{Warning:}$ You cannot just use Vieta to conclude your answer since we are asked for sum of $\textbf{real}$ roots.