7. Let $P(n)$ denote the product of all non-zero digits of the positive integer $n$, for example: $P(123)=1 \times 2 \times 3=6$, $P(206)=2 \times 6=12$. Then $P(1)+P(2)+\cdots+P(999)=$ $\qquad$ —.
【Answer】 97335