For hydrazoic acid, which of the following resonating structure will be least stable?

$$\begin{gathered} \mathrm{H}-\mathrm{N}=\stackrel{+}{\mathrm{N}}=\stackrel{-}{\mathrm{N}}\leftrightarrow \mathrm{H}-\stackrel{+\dot{}}{\mathrm{N}}-{\mathrm{N}}^{+}={\mathrm{N}}^{2-}\leftrightarrow \mathrm{H}-\overline{\mathrm{N}}-\stackrel{+}{\mathrm{N}}\equiv \mathrm{N} \\ \left(\mathrm{I}\right) \left(\mathrm{II}\right) \left(\mathrm{III}\right) \end{gathered}$$