An algebra problem by Priyanshu Mishra

Let $f: \mathbb R \rightarrow \mathbb R$ for all reals $x, y$ such that

$\large f( x+y ) + f( x )f( y ) = f( x ) + f( y ) + f( xy ) .$

If only one non-constant function exists satisfying above relation, find $f(2017)$ .

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Notation: $\mathbb R$ denotes the set of real numbers .