Notice that this problem involves the addition of a number "1" per consecutive pair (a number minus the integer that immediately precedes it), so it adds "1" (one) every couple of consecutive numbers.
2018 - 2017 = 1
2016 - 2015 = 1
...
4- 3 = 1
2 - 1 = 1
That means it is the addition of 2018/2 = 1009 numbers "1". This clearly results on the number 1009, which is an odd number.
