2011*(1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90)
=2011(1/1-1/2+1/2-1/3+1/3-1/4+...+1/8-1/9+1/9-1/10)
=2011(1/1-1/10)
=2011*9/10
=1809.9