10. Calculate:
$$
325 \times\left(\frac{1}{1 \times 2 \times 3 \times 4}+\frac{1}{2 \times 3 \times 4 \times 5}+\frac{2}{4 \times 5 \times 6 \times 7}+\frac{2}{5 \times 6 \times 7 \times 8}+\cdots+\frac{8}{22 \times 23 \times 24 \times 25}+\frac{8}{23 \times 24 \times 25 \times 26}\right)
$$
$18$