Redox Reactions

What is the stoichiometric coefficient of $ \mathrm{SO}_{2} $ in the following balance reaction?

$ \mathrm{MnO}_{4}^{-}(a q)+\mathrm{SO}_{2}(\mathrm{~g}) \longrightarrow \mathrm{Mn}^{2+}(a q)^{-}+\mathrm{HSO}_{4}^{-}(a q) $

(in acidic solution)