1,-2,3,-4,5,-6,7,-8…… What is the number 2004 and the number 2005?

1,-2,3,-4,5,-6,7,-8…… What is the number 2004 and the number 2005?

The number increases naturally, and the sign is odd positive and even negative
The number 2004 is even, so it's - 2004
The number 2005 is odd, so it's 2005