Solution
= Solution
The vertices $v_2,v_3,v_5$ form a <triangle in a graph>, so every <cut of a graph> leaves at least one of their three edges uncut. Hence the cut size is at most four. Take
$$
S_1=\{v_2,v_5\},
\qquad
S_2=\{v_1,v_3,v_4\}.
$$
The crossing edges are $(1,5),(2,3),(3,5),(4,5)$, so $C=4$. The upper bound is attained and this is a <maximum cut>.