3. Let $[x]$ denote the greatest integer not exceeding $x$. If
$$
\begin{array}{l}
f=[1 \mathrm{~g} 1]+[1 \mathrm{~g} 2]+[1 \mathrm{~g} 3]+\cdots+[1 \mathrm{~g} 1989] \\
+[1 \mathrm{~g} 1990], \text { then } f=
\end{array}
$$
3. $4863 ;$