(1-1 / 2005) + (1-1 / 2005 × 2) + (1-1 / 2005 × 3) +... + (1-1 / 2005 × 2004) + (1-1 / 2005 × 2005),

(1-1 / 2005) + (1-1 / 2005 × 2) + (1-1 / 2005 × 3) +... + (1-1 / 2005 × 2004) + (1-1 / 2005 × 2005),

Put forward one, there are 2005 ones, so
=2005-【(1+2+3+...+2005)/2005】
=2005-1003
=1002