Compute the value of
\(1 - 2 + 3 - 4 + \dots + 2019 - 2020 + 2021\).
\(\begin{array}{|rcll|} \hline s &=& 1 - 2 + 3 - 4 + \dots + 2019 - 2020 + 2021 \\ s&=& 2021 - 2020 +2019 - \dots -4+3-2+1 \\ \hline 2s &=& 2022-2022+2022-2022 + \dots + 2022-2022+2022 \\ 2s &=& 0+0+ \dots +0+2022 \\ 2s &=& 2022 \\ s &=& 1011 \\ \hline \end{array}\)
\(1 - 2 + 3 - 4 + \dots + 2019 - 2020 + 2021 = \mathbf{1011} \)