4. Let $f(x)=x^{4}+a x^{3}+b x^{2}+c x+d$, where $a, b, c, d$ are constants. If $f(1)=$ $1, f(2)=2, f(3)=3$, then the value of $f(0)+f(4)$ is $\qquad$ .
4. 28 .

Let $g(x)=f(x)-x$, then $g(1)=g(2)=g(3)=0$, so $g(x)=(x-1)(x-2)(x-$ 3) $(x-r)$ (where $r$ is a constant), then $f(4)+f(0)=g(4)+4+g(0)=6(4-r)+4+6 r=28$.