(2000-1990+1980-1970+...+20-10)/[(1-1/2)x(1-1/3)x(1-1/4)x...x(1-1/999)x(1-1/1000)]
=(10+10+10+...+10)/(1/2x2/3x3/4x.x998/999x999/1000)
=(10x100)/(1/1000)
=1000x1000
=1000000