9. Observe first, then fill in the blanks.
\[
\begin{array}{l}
9 \times 9+19=100 \\
99 \times 99+199=10000 \\
999 \times 999+1999=1000000
\end{array}
\]
\(\underbrace{999 \cdots 99}_{2020 \text { nines }} \times \underbrace{999 \cdots 99}_{2020 \text { nines }}+1 \underbrace{999 \cdots 99}_{2020 \text { nines }}\) has \(\qquad\) zeros at the end.
$4040$