# Birthday Problem!

Algebra Level 5

$\large \displaystyle f(x+y) \leqslant yf(x)+f(f(x))$

Let $$f:\mathbb{R} \rightarrow \mathbb{R}$$ be a real-valued function defined as shown above for all real numbers $$x$$ and $$y$$. Find $$\displaystyle f(-5699)$$.

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