To find the sum of the given sequence, we can group the numbers into pairs that add up to zero.

We have (-1) + 1 = 0, (-2) + 2 = 0, and so on, until (-98) + 98 = 0.

So, all the numbers from -1 to -98 will cancel out with their corresponding positive numbers, leaving us with only 99 and 100.

Therefore, the sum of the given sequence is 99 + 100 = 199.