3. Let $f(x)$ be an odd function defined on $\mathbf{R}$, $f(1)=2$, when $x>0$, $f(x)$ is an increasing function, and for any $x, y \in \mathbf{R}$, we have $f(x+y)=f(x)+f(y)$, then the maximum value of the function $f(x)$ on $[-3,-2]$ is
It is known that $f(x)=2 x$, so the maximum value of $f(x)$ on $[-3,-2]$ is -4.