Let a function \( f:\mathbb{R}\to\mathbb{R} \) be defined asWhere \( [ x ] \) is the greatest integer less than or equal to \( x \). If \( f \) is continuous on \( \mathbb{R} \), then \( (a+b) \) is equal to:
\( 4 \)
\( 3 \)
\( 2 \)
\( 5 \)