I am trying to solve the functional equation:

> 
> Find all functions $f:\mathbb R^2\rightarrow \mathbb R$ such that for all $\left \{x\_1,x\_2,...,x\_{2016} \right \}\subset \mathbb R$:
>  $$f(f(f(...(f(x\_1,x\_2),x\_3),...),x\_{2016}))=x\_1+x\_2+...+x\_{2016}$$
> 
> 
> 

**My work so far:**

$f(x,y)=f(0+0+..+0+x,y)$

$f(f(f(...(f(0,0),0),...),x),y)=0+0+...+0+x+y=x+y$

I need help here.