G2.2 If $S_{n}=1-2+3-4+\ldots+(-1)^{n-1} n$, where $n$ is a positive integer, determine the value of $S_{17}+S_{33}+S_{50}$.
If $n=2 m$, where $m$ is a positive integer,
$$
\begin{array}{l}
S_{2 m}=(1-2)+(3-4)+\ldots+(2 m-1-2 m)=-m \\
S_{2 m+1}=-m+2 m+1=m+1 \\
S_{17}+S_{33}+S_{50}=9+17-25=1
\end{array}
$$