If \[ \sqrt[3]{i} = \operatorname{cis}\alpha,\qquad \alpha \text{ belongs to the second quadrant} \] and \[ \sqrt[3]{-i} = \operatorname{cis}\beta,\qquad \beta \text{ belongs to the third quadrant} \] then find \[ \operatorname{cis}\alpha + \operatorname{cis}\beta = \, ? \]