document.write('
1000-11-89-12-88-13-87-14-86-15-85-16-84-17-83-18-82-19-81
=1000-(11+89)-(12+88)-(13+87)-(14+86)-(15+85)-(16+84)-(17+83)-(18+82)-(19+81)
=1000-100×9
=100