# Based on the IMO

Algebra Level 5

$f\left( x+a \right) \le af\left( x \right) +f\left( f\left( x \right) \right)$

A function $$f\left( x \right)$$ is defined for all real numbers $$x$$ and returns a real number for every input $$x$$ (That is, $$f: \mathbb R\rightarrow \mathbb R$$). The above describes this function, where $$a$$ is a real number. What is the value of $$f\left( -1 \right)$$?

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