# 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 \(f\left( -1 \right) \)?