8 Let two non-zero vectors $\vec{a}$ and $\vec{b}$ in the plane be perpendicular to each other, and $|\vec{b}|=1$, then the sum of all real numbers $m$ that make the vectors $\vec{a}+m \vec{b}$ and $\vec{a}+(1-m) \vec{b}$ perpendicular to each other is